[CentOS] yum libxml2mod

I have a problem using yum. it gives me the following error

[root at mail1 src]# yum update yum
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   /usr/lib/python2.3/site-packages/libxml2mod.so: undefined symbol: 
xmlNewDocPI

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, Mar 10 2006, 06:12:09)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)]

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

I have looked in Internet and others forums but i couldn't find any 
answer on how to fix this error.