Prime95 errors are usually caused by CPU or memory problems. Try lowering you OC, raising your voltages, and increasing your CPU cooling. IF you pushed the FSB and got the error, and still got the error when you lowered the mem speed, the problem is probably your CPU. Once again, try more volts and better cooling (if you need to). If those don't work, lower the overclock.
edit: check the intel forum for reasonaable and "safe" voltages, as increasing voltage can be dangerous to your CPU. In all cases, increasing voltage will shorten the life of your CPU (however, a modest increase will not likely do so significently), as it increases the rate of electromigration.