mono-data-firebird
mono-data-sybase
mono-jscript

was deprecate since mono-2.8 more info in http://www.mono-project.com/Release_Notes_Mono_2.8#Removed_Libraries_and_Commands

I suggest uninstall that packages and try update again.

mono-2.10.8-3.el6 has been submitted as an update for Fedora EPEL 6.
https://admin.fedoraproject.org/updates/mono-2.10.8-3.el6

Package mono-2.10.8-3.el6:
* should fix your issue,
* was pushed to the Fedora EPEL 6 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=epel-testing mono-2.10.8-3.el6'
as soon as you are able to.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-EPEL-2014-1798/mono-2.10.8-3.el6
then log in and leave karma (feedback).

Sorry for the delay in testing; I just realized that my repo priorities were preventing me from seeing the updated packages in epel-testing.

I verified that manually removing those deprecated packages allows the released 2.10.8-2 updates to install.  One system I tested on also had "mono-moonlight" installed, which also needed to be removed.  Looks like that's also obsoleted by the new mono-core-2.10.8-3 (though wasn't yet in 2.10.8-2).

However when I try testing the 2.10.8-3 packages in epel-testing on another system that still has the deprecated packages installed, it seems like the obsoletes you added aren't working for some reason.  Shouldn't the obsoletes cause yum to add the removal of those obsoleted packages to the transaction? That is not happening, and the transaction still fails due to the broken dependencies for those deprecated pacakges:

# yum update --enablerepo=epel-testing --disableplugin=priorities mono-core-2.10.8-3.el6
Loaded plugins: aliases, auto-update-debuginfo, product-id, protectbase, refresh-packagekit,
              : subscription-manager
Updating Red Hat repositories.
0 packages excluded due to repository protections
Setting up Update Process
Resolving Dependencies
--> Running transaction check
---> Package mono-core.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: libmono-profiler-logging.so.0()(64bit) for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: libmono.so.0()(64bit) for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: libmono.so.0(VER_1)(64bit) for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Commons.Xml.Relaxng) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(ICSharpCode.SharpZipLib) = 0.84.0.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(ICSharpCode.SharpZipLib) = 0.84.0.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Cecil) = 0.6.9.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.CompilerServices.SymbolWriter) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.GetOptions) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.GetOptions) = 2.0.0.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Posix) = 1.0.5000.0 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Posix) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Posix) = 1.0.5000.0 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Security) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Security) = 1.0.5000.0 for package: mono-data-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Security) = 1.0.5000.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Mono.Security) = 1.0.5000.0 for package: mono-data-postgresql-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-oracle-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-postgresql-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Xml) = 1.0.5000.0 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Xml) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Xml) = 1.0.5000.0 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Xml) = 1.0.5000.0 for package: mono-data-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Xml) = 1.0.5000.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-oracle-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-postgresql-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-sqlite-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-web-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-winforms-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-oracle-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-wcf-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-devel-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-web-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-extras-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-postgresql-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-sqlite-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-jscript-2.4.3.1-4.el6.x86_64
---> Package mono-core.x86_64 0:2.10.8-3.el6 will be an update
--> Running transaction check
---> Package mono-core.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-jscript-2.4.3.1-4.el6.x86_64
---> Package mono-data.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(Mono.Data.Tds) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Data) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Data) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.EnterpriseServices) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
---> Package mono-data.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-data-oracle.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-data-oracle.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-data-postgresql.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-data-postgresql.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-data-sqlite.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-data-sqlite.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-devel.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-devel.x86_64 0:2.10.8-3.el6 will be an update
--> Processing Dependency: mono(monodoc) = 1.0.0.0 for package: mono-devel-2.10.8-3.el6.x86_64
---> Package mono-extras.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(Microsoft.Vsa) = 7.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Microsoft.Vsa) = 8.0.0.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
---> Package mono-extras.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-wcf.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-wcf.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-web.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-web.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-web-devel.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-web-devel.x86_64 0:2.10.8-3.el6 will be an update
---> Package mono-winforms.x86_64 0:2.4.3.1-4.el6 will be updated
---> Package mono-winforms.x86_64 0:2.10.8-3.el6 will be an update
--> Running transaction check
---> Package mono-core.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Drawing) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(mscorlib) = 1.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono-core = 2.4.3.1-4.el6 for package: mono-jscript-2.4.3.1-4.el6.x86_64
---> Package mono-data.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(Mono.Data.Tds) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Data) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.Data) = 1.0.5000.0 for package: mono-data-firebird-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(System.EnterpriseServices) = 1.0.5000.0 for package: mono-data-sybase-2.4.3.1-4.el6.x86_64
---> Package mono-extras.x86_64 0:2.4.3.1-4.el6 will be updated
--> Processing Dependency: mono(Microsoft.Vsa) = 7.0.5000.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
--> Processing Dependency: mono(Microsoft.Vsa) = 8.0.0.0 for package: mono-jscript-2.4.3.1-4.el6.x86_64
---> Package monodoc.x86_64 0:2.10.8-3.el6 will be installed
--> Finished Dependency Resolution
Error: Package: mono-data-firebird-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System.Drawing) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System.Drawing) = 1.0.5000.0
               mono(System.Drawing) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System.Drawing) = 4.0.0.0
               mono(System.Drawing) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System.Drawing) = 4.0.0.0
               mono(System.Drawing) = 2.0.0.0
Error: Package: mono-data-firebird-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(mscorlib) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(mscorlib) = 1.0.5000.0
               mono(mscorlib) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
Error: Package: mono-data-firebird-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System.Data) = 1.0.5000.0
           Removing: mono-data-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System.Data) = 1.0.5000.0
               mono(System.Data) = 2.0.0.0
           Updated By: mono-data-2.10.8-3.el6.x86_64 (epel-testing)
               Not found
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
           Available: mono-core-2.10.8-3.el6.i686 (epel-testing)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               Not found
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
Error: Package: mono-jscript-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(Microsoft.Vsa) = 7.0.5000.0
           Removing: mono-extras-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(Microsoft.Vsa) = 7.0.5000.0
               mono(Microsoft.Vsa) = 8.0.0.0
           Updated By: mono-extras-2.10.8-3.el6.x86_64 (epel-testing)
               Not found
Error: Package: mono-jscript-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(mscorlib) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(mscorlib) = 1.0.5000.0
               mono(mscorlib) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
Error: Package: mono-data-firebird-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System) = 1.0.5000.0
               mono(System) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
Error: Package: mono-jscript-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono-core = 2.4.3.1-4.el6
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono-core = 2.4.3.1-4.el6
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono-core = 2.10.8-3.el6
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono-core = 2.10.8-2.el6
Error: Package: mono-data-firebird-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono-core = 2.4.3.1-4.el6
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono-core = 2.4.3.1-4.el6
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono-core = 2.10.8-3.el6
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono-core = 2.10.8-2.el6
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(mscorlib) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(mscorlib) = 1.0.5000.0
               mono(mscorlib) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(mscorlib) = 4.0.0.0
               mono(mscorlib) = 2.0.0.0
Error: Package: mono-jscript-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System) = 1.0.5000.0
               mono(System) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
Error: Package: mono-jscript-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(Microsoft.Vsa) = 8.0.0.0
           Removing: mono-extras-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(Microsoft.Vsa) = 7.0.5000.0
               mono(Microsoft.Vsa) = 8.0.0.0
           Updated By: mono-extras-2.10.8-3.el6.x86_64 (epel-testing)
               Not found
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System.Data) = 1.0.5000.0
           Removing: mono-data-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System.Data) = 1.0.5000.0
               mono(System.Data) = 2.0.0.0
           Updated By: mono-data-2.10.8-3.el6.x86_64 (epel-testing)
               Not found
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
           Available: mono-core-2.10.8-3.el6.i686 (epel-testing)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               Not found
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System.Data) = 4.0.0.0
               mono(System.Data) = 2.0.0.0
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono-core = 2.4.3.1-4.el6
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono-core = 2.4.3.1-4.el6
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono-core = 2.10.8-3.el6
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono-core = 2.10.8-2.el6
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System.EnterpriseServices) = 1.0.5000.0
           Removing: mono-data-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System.EnterpriseServices) = 1.0.5000.0
               mono(System.EnterpriseServices) = 2.0.0.0
           Updated By: mono-data-2.10.8-3.el6.x86_64 (epel-testing)
               Not found
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System.EnterpriseServices) = 4.0.0.0
               mono(System.EnterpriseServices) = 2.0.0.0
           Available: mono-core-2.10.8-3.el6.i686 (epel-testing)
               mono(System.EnterpriseServices) = 4.0.0.0
               mono(System.EnterpriseServices) = 2.0.0.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               Not found
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System.EnterpriseServices) = 4.0.0.0
               mono(System.EnterpriseServices) = 2.0.0.0
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(Mono.Data.Tds) = 1.0.5000.0
           Removing: mono-data-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(Mono.Data.Tds) = 1.0.5000.0
               mono(Mono.Data.Tds) = 2.0.0.0
           Updated By: mono-data-2.10.8-3.el6.x86_64 (epel-testing)
               mono(Mono.Data.Tds) = 4.0.0.0
               mono(Mono.Data.Tds) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(Mono.Data.Tds) = 4.0.0.0
               mono(Mono.Data.Tds) = 2.0.0.0
           Available: mono-core-2.10.8-3.el6.i686 (epel-testing)
               mono(Mono.Data.Tds) = 4.0.0.0
               mono(Mono.Data.Tds) = 2.0.0.0
           Available: mono-data-2.10.8-2.el6.x86_64 (epel)
               mono(Mono.Data.Tds) = 4.0.0.0
               mono(Mono.Data.Tds) = 2.0.0.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               Not found
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(Mono.Data.Tds) = 4.0.0.0
               mono(Mono.Data.Tds) = 2.0.0.0
Error: Package: mono-data-sybase-2.4.3.1-4.el6.x86_64 (@epel/6.2)
           Requires: mono(System) = 1.0.5000.0
           Removing: mono-core-2.4.3.1-4.el6.x86_64 (@epel/6.2)
               mono(System) = 1.0.5000.0
               mono(System) = 2.0.0.0
           Updated By: mono-core-2.10.8-3.el6.x86_64 (epel-testing)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
           Available: mono-core-2.10.8-2.el6.i686 (epel)
               mono(System) = 4.0.0.0
               mono(System) = 2.0.0.0
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

mono-2.10.8-4.el6 has been submitted as an update for Fedora EPEL 6.
https://admin.fedoraproject.org/updates/mono-2.10.8-4.el6

2.10.8-4 in testing successfully resolves the problem.  The obsoleted packages are cleanly removed, and all updates can install without errors.

Positive karma registered in Bodhi.

Thanks.

mono-2.10.8-4.el6 has been pushed to the Fedora EPEL 6 stable repository.  If problems still persist, please make note of it in this bug report.