[Yum] Yum problem

[simon jones]

Hi, does anyone know how to fix the following error:

[root at nas01 /]# yum upgrade
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:
2.3.4 (#1, Feb 22 2005, 04:09:37) 
[GCC 3.4.3 20041212 (Red Hat 3.4.3-9.EL4)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://wiki.linux.duke.edu/YumFaq

Thanks!