Fedora 14 yum update issue.

I upgrade F13 to F14 and have problems to update one.

yum-3.2.28-3.fc13.noarch
Fedora release 14 (Branched)


And repolist is.

There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   No module named yum

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.7 (r27:82500, Jul 26 2010, 18:19:50)
[GCC 4.5.0 20100716 (Red Hat 4.5.0-3)]

If you cannot solve this problem yourself, please go to
the yum faq at:
  http://yum.baseurl.org/wiki/Faq

And error msg.

The backend exited unexpectedly. This is a serious error as the
spawned backend did not complete the pending transaction.

Any ideas? Cheers.