Check your miners - some people are reporting that they're seeing invalid shares start showing up after the miner has been running for a long time. I haven't been able to replicate this yet on any of my machines, but I'm looking.
yupe, 3 in a row after you mentioned it.
4 hrs after I started 2 instances of xptminer on 2 different machines, I noticed a chain of "Reason: CheckProofOfWork() : n not prime" on my I7 4770, compiled to AVX. My other machine, Quad core Q9550, compiled to SSE, no chain of msg yet.
I've had this too on dga's official b11 Windows build. It just stops finding valid shares altogether and always says "n not prime" for any share found.
Are people seeing this on Linux also?