I wanted to post this on a nice forum, so the information can be found by others. I help run a small PC repair company.
I've had 3 systems come in this week with this exact problem- a BSOD 0x50 ( 0x00000050) randomly in Windows XP, and 7. I dont think the problem is OS related.
After countless hours in Memtest, one of the 3 systems had bad memory, but 20 passes found 3 faults. Memory swapped out.
I ran Combofix, Stinger, RKill, TDSS Killer, Malwarebytes, AVG.... They each picked up a few things, but the BSODs kept coming. 2 of the 3 systems would shut down (like I had hit a software shutdown button) when IE was opened. Resetting IE 8/9 fixed this.
I went to OSR Online (you can Google it) and loaded in the most recent dump file- They are located in C:\Windows\Minidumps.
This was able to pinpoint the driver at fault- In all 3, it was a legitimate driver. I then went into Regedit, killed off all mentions (except one, it was a Windows driver- I ran a repair installation after deleting the file manually). This fixed the problem, as far as I can tell. Obviously, whatever was killed needs to be forgotten or reinstalled. But killing it is certainly necessary- On one system, even a repair installation did not fix the problem when a Windows driver was found to be at fault.
I post here because I believe this isn't a coincidence, this is a new infection which has not been identified yet. This was how I found and fixed the problem, I hope your Google searches bring you here! Good luck, folks!