After using up2date to update up2date to version 2.5.3-0.6.x it fails with the following message. There was a fatal RPM error. The message was: Couldn't determine what version of Red Hat Linux you are running. I have checked the up2date.py file and believe the problem is on line 234 where it checks the RPM database for a package that provides redhat-release and while redhat-release has the file /etc/redhat-release i believe this looks for virtual providers and since nothing provides redhat-release, as confimed by "rpm -q --whatprovides redhat-release", up2date can't find the redhat-release rpm and thus can't find the RedHat version. There is an interum solution to people experiencing this problem, edit /etc/sysconfig/rhn/up2date and set versionOverride to your RedHat version until a new up2date fixes the problem.
This is a side-effect of the upgrade to rpm-4.0.2 . . . to resolve the issue, just run 'rpm --rebuilddb' as root and things will start working again.
I had the same problem on my redhat 7.3 box: when using rhn_register, the program crashed and I got the "Couldn't determine version" error message. The rhn_register version is 2.7.21-7.x.3 and the rpm version is 4.0.4-7x.18 I tried the rpm --rebuilddb command but it did not work ( I have not upgraded anything yet ) I edited /etc/sysconfig/rhn/up2date file but it still does not work. I removed many rpms to get a light system, maybe the problem comes from that ?