I agree with Klassje. It is likely that a riser is bad. Old, skinny-version risers get really hot and sometimes melt with dual-mining, and even new risers go bad. It is interesting to note that if the problem occurs, the "511C" figure is common. I have had the same readout; the card was good but the riser was bad. I would stop the rig and change risers before mining again. --scryptr