I know it's been a bit since this was replied to, but since I didn't think that starting a new thread for this would be warranted, I post here.
I've been having the same problem, and I've noticed that the 174.xx drivers don't list nVidia 7xxx series chipsets as being supported. I'm currently running the latest 169.xx driver set for my 7900GS and I get this problem repeatedly. Would installing 174.xx drivers be advised?