Because of limitations for our yum plugin on S.L. 4.x, installing openafs often installs the wrong kernel module. Yum is perfectly fine afterwards for updating both openafs and/or your kernel, but the initial yum install of openafs can sometimes go wrong.
We are working on fixing this. When we do, these commands will change.

The following command will get the basic openafs installed, enough to get openafs running on your system. If you need to add more components, such as openafs-krb5, simply add them to the following command, and/or do another yum install of just those components.
Do a cut and paste of the following command.

yum install openafs-client kernel-module-openafs-`uname -r`