Ouch! I hope you are charging $150/hr to fix the laptop of this clueless user? Have you looked in the system logs to see what errors are being written? This error message has several causes, some of which can be easy to track down - others not. You could spend the time tracking the cause down, but I suspect you will find more than 1 problem, since you have no idea what this idiot has done to the system. One idea from left field is they might have modified the security settings and PAM is kicking the user out before it can login. So I recommend instead, you simply wipe the sytem and reinstall CentOS5, and tell the user not to touch anything they don't know about.