could be a heat shutdown, but more than likely you're gonna have to raise your voltage a LITTLE bit. don't raise the voltage too much because it is the direct cause of heat/overheat.
i would say that much over 2.8 is going to become more of a problem than it is worth, generally around +20% is the line where heat becomes a big player, and you have to consistently jump the voltage to maintain stability.
Make sure that your ram can handle the raised FSB and that you're supplying it with enough voltage as well.
running stock cooling? might consider something copper based if your temps are hanging around the 50C level.
good luck