OP, what time did you bring down the pool? I was at home about 3 hours ago and saw my miner is dead with invalid user and prehash-stale errors. I restarted it and confirmed it has 28 kh/s then I left ... Didnt double check if it went back to full speed....  now I am at my office and saw its dead again with 0 kh/s.

Ok, i just restarted my two machines now they seem to work fine. Hopefully they will be stable for the next 7 hours before i go to bed