Windows XP error messages cripples my comp

Recently I have been getting an error message that says "The procedure entry point EndDialog could not be located in the dynamic link library User32.dll."

This will happen at random times with no apparent program it seems to be related to specifically. I will be trying to open up "my computer" and this will stop me and prompt me to send an error report. When I was trying to get my live updates for window it also prevented me from downloading them. Even when I try to open internet explorer it stops me cold with an error report message prompt. Afterward it will keep poping up error report messages and I have no way to stop it except restarting.

If anyone can help I would greatly appreciate it.

If it helps I have CWShredder, Hijackthis, spybot, and adaware from a previous time when you guys were so kind to help me.