That's what happens when the card or pool (or combination of the 2) freaks out from too much OC. I eventually had to just completely disable OC while mining JPC, or else this would happen about once a day. And if it happens while you're asleep, you get several hours of mining at half hash rate. Further back in this thread is a way to compile ccminer to exit and reboot when this happens, but that's a bit over my head and I'm just waiting for it to be incorporated into a future release.