I had a Nvidia GeForce 9800 GX2 (unclocked) with a similar type of message appearing now and again, games would freeze then display the message and crash out or graphics would become garbled while playing.
Here's a link to the Nvidia forum where others had the same message (click here)
This behaviour occurred at random for a year or more and finally last week the card stopped working with games at all, the 2D worked OK but 3D for games and AERO on Windows 7 were borked. I myself believe the card was overheating while playing games and eventually gave up the ghost. Checking the GPU temperature while running a game may give you some idea if this is the cause.