First thing you do is search the forums for your error. You should be doing that before you post in fact. edit: And I do hope folks answering these questions are doing the same.
Although in this case the problem is probably memory, although in this case it;s probably video memory.
What specific video card are you running? And how much video memory does it have?
There was also a patch way back when that upgraded directx v9 which is only required if you run into errors. For whatever reason, microsoft didn't push it out via update. Let me go find the download link.
I have been playing the game successfully for 6 weeks with NO errors. I received my first error 5 days ago. I have a 64 bit OS I have a ATI radeon 3000 with 2 Gigs of video memory, I also searched the forums for my error and found nothing, I do appreciate you brain storming on why this might be happening so Thank you very much!