I upgraded my Redhat 6.0 system from local hard drive. Somehow, when I was ftping all the RPMs a few went missing, and so my copy of Red Hat was incomplete. The upgrade script crashed in a confusing way, throwing incomprehensible Python stack trace. It would have been more helpful to have an English error message. I believe this bug is in the same general class as #6159: a corrupted RPM repository not handled gracefully by the installer.
*** This bug has been marked as a duplicate of 6159 ***