Had to rebuild a system recently and while stress testing it i decided to get the graphics card to 'fold' to stress the system a bit. Before the end of any of the work units it would return with 'unstable_machine' error. Tried the Stanford gpu mem tester and it came back with thousands of errors over the course of the 50 loop cycle. I installed evga precision tool and after a couple of trials found that if i knocked the memory speed down from 1125 to 1083 i got no more errors on the test. The card, a 9800gtx BFG overclock version, now folds units fine. Just thought i would share the info.