The point about deleting the content of the DAT folder was nothing to do with an out of date file, rather a corrupted one. That way the file got purged and replaced. I would try it at least. Update immediately afterwards, or click "Fix".
Often the only route is to do the uninstall, MCPR removal tool routine and then reinstall. It cures a lot of issues. I would try that too.
Have you been using any registry cleaners lately? They cause havoc with programmes like McAfee.
It's the weekend now so there is only us volunteers available here. The Technical Support Chat is free and available 24/7. At least they can escalate the issue.
By the way, in less than 1 years time XP SP2 will be obsolete so I recommend you upgrade to SP3 a.s.a.p. There is help with that here:
http://community.mcafee.com/showthread.php?t=220807