From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; de; rv:1.8.0.7) Gecko/20061011 Fedora/1.5.0.7-7.fc6 Firefox/1.5.0.7

Description of problem:
Component: yumex
Version: 1.1.7
Summary: TB58bd9c01 yumexBase.py:229:doRepoSetup:RepoError: Cannot open/read repomd.xml file for repository: core-source

Traceback (most recent call last):
  File "/usr/share/yumex/yumexmain.py", line 137, in on_pkgProcess_clicked
    self.on_queueProcess_clicked( widget )
  File "/usr/share/yumex/yumexmain.py", line 184, in on_queueProcess_clicked
    self.yumexbase.reset_ts()
  File "/usr/lib/python2.4/site-packages/yumex/yumexBase.py", line 124, in reset_ts
    self.doUpdateSetup()
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 353, in doUpdateSetup
    self.doRepoSetup()
  File "/usr/lib/python2.4/site-packages/yumex/yumexBase.py", line 229, in doRepoSetup
    raise Errors.RepoError, ( 'Cannot open/read repomd.xml file for repository: %s' % repo )
RepoError: Cannot open/read repomd.xml file for repository: core-source

Local variables in innermost frame:
e: failure: repodata/repomd.xml from core-source: [Errno 256] No more mirrors to try.
thisrepo: None
repos: [<yum.yumRepo.YumRepository object at 0x8a918ec>, <yum.yumRepo.YumRepository object at 0x8a91f6c>, <yum.yumRepo.YumRepository object at 0x89efb8c>, <yum.yumRepo.YumRepository object at 0x8a917cc>]
repo: core-source
num: 1
self: <yumex.yumexBase.yumexBase object at 0x860acac>


Version-Release number of selected component (if applicable):
yumex-1.1.7-1.0.fc6

How reproducible:
Always


Steps to Reproduce:
1. Run yumex
2. Add core-source repository
3.

Actual Results:
Yumex exits with an unhandled exception error (see above)

Expected Results:
Yumex should've received the file repomd.xml

Additional info:
It appears that the URL Yumex is looking for the file repomd.xml is incorrect:
Yumex looks for http://redhat.download.fedoraproject.org/pub/fedora/linux/core/6/SRPMS/repodata/repomd.xml

<snip>

Trying other mirror.
Preparing for install/remove/update
--> Preparing for install
Loading Repositories Data : Init. core-source repository
Determining fastest mirrors for core-source
--> Mirrors Detected (Top 3)
---> http://redhat.download.fedoraproject.org/pub/fedora/linux/core/6/SRPMS/
Failure getting http://redhat.download.fedoraproject.org/pub/fedora/linux/core/6/SRPMS/repodata/repomd.xml: 
  --> [Errno 14] HTTP Error 404: Date: Sat, 28 Oct 2006 08:05:36 GMT
  --> Server: Apache
  --> Transfer-Encoding: chunked
  --> Content-Type: text/html

</snip>

However, the actual URL appears to be 
http://redhat.download.fedoraproject.org/pub/fedora/linux/core/6/source/SRPMS/repodata/