C000021a {Fatal System Error}

XP Pro SP2. The error message also mentions something about the login encountered an error and restarted the system. I haven't spent too much time researching this, but the little bit of searching I've done hasn't told me much about the cause, and nothing about a fix. I tried a repair install and it went great right up until the very end. The error comes up right after the XP logo and scrolling progress bar disappear, right before the blue Welcome screen.
Any suggestions?

 

If anyone gives a :crap the problem turned out to be a bad memory stick. I had run 2 different diagnostics: 8 passes (17 tests per pass) with one, and the other I ran overnight and neither diagnostic found any problems with the RAM. As soon as I removed the stick and installed a different one, the problems disappeared and the PC is now running perfectly.
:confused
Strange.

 

I used one of the MemTests (a bootable one; it's the one on the Ultimate Boot CD) and the bootable Microsoft Memory Diagnostic (which is also available on the Ultimate Boot CD and also on the Vista install disc). I usually get really accurate info from the MS test and I use it almost daily; I don't use Memtest very often....