Did mining difficulty or anything else changed after the fork? I haven't been able to check my miner rig for a few days, and now I see that it didn't hit the block for an unusually long time. I wonder if this has anything to do with the hard fork...
This was a mandatory update, we had a hard fork at block 375,000. All the old wallet versions either got stuck at that block or ended up on a fork. If you're mining on an old version of the wallet stop immediately and upgrade otherwise your mining power is wasted.