Missing dll

I just followed your excellent malware removal guide to clean up my mother's poor machine which is running XP. The computer is running perfectly but whenever you turn it on there is a message that C:\WINDOWS\system32\jcftrjbx.dll is missing or could not be found. A google search for this error produced only a handful of ads for repairing dll's. I am unsure whether the missing dll is really something I want to repair, if so how to do it, and if not, how to get the message to stop appearing and scaring my mother. Thanks for any help and advice!