After updating my server from CentOS 4.8 to CentOS 5.4, I noticed that yum cannot work as before, here's the error message:

Code:
[root@admon CentOS-5up]# yum clean all
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   No module named sqlite

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:
2.4.3 (#1, Sep  3 2009, 15:37:12) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-46)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://wiki.linux.duke.edu/YumFaq
After google around, this issue got fixed by re-install python-sqlite like this:

Code:
[root@admon CentOS-5up]# rpm -Uvh python-sqlite-1.1.7-1.2.1.i386.rpm --force
Preparing...                ########################################### [100%]
   1:python-sqlite          ########################################### [100%]
[root@admon CentOS-5up]# yum clean all
Repository base is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Cleaning up Everything