For years I ignored this problem with my ATi Radeon 9200 128mb graphics card by using an older card from my older computer. Recently I purchased a new graphics card, ATi Radeon X700 256mb, and this problem appeared once again.
The problem arises when the card is subjected to a high level performance game (eg Diablo II, or any graphically intense game). The basic problem is that the Video Card would no longer respond to its respected Driver.
From reading other sites, some possible causes of error are:
-Not Enough Power is given to the Graphics Card
-Graphics Card Overheats