error going into user accounts

When my grandchildren's computer is started and gets to the user account page, there is an error message as follows.

"The system could not log you on. Make sure your user name and domain are correct, then type your password again. Letters in passwords must be typed using the correct case. OK"

They click OK, then the user accounts come up like they should. Is there any way to stop this?

They have XP Home.

Thanks
Peg

 

Wait, are you saying that they're able to login without typing in a password when there is a password? Or when it starts up does it automatically show that error message?

 

It shows the error just as the user sign-in comes up but before a password can be typed in.

 

That's really weird... you could have some sort of program that runs on the system when it starts up and makes strange stuff... it may be a virus or something; get a HijackThis log on here and someone with virus knowledge will be able to help you out.