[Yum] yum error before upgrade of Fedora

[Marcos Roberto Silva]

Hi all.
After I upgraded my Fedora Core 3 to Fedora Core 4, the yum reports the 
error below:

[root at Marcos ~]# yum update
The yum libraries do not seem to be available on your system for this 
version of python  2.4.1 (#1, May 16 2005, 15:19:29)
[GCC 4.0.0 20050512 (Red Hat 4.0.0-5)]
Please make sure the package you used to install yum was built for your 
install of python.
[root at Marcos ~]#

Could someone please help me?
Thanks,

Marcos