There is an ongoing problem with Win64 and PS3grid. It seems there is a memory leak (somewhere...), which after anywhere from a few days to a week or so, will cause the GPU wu's to fail. The solution to date is to re-boot the machine (early and often).

I missed my scheduled re-boot the other day, and so lost the ability to crunch for about a day. The loss of time is due to the daily limit of 6 (or is it 8??) wu's per cpu, which I errored out in around 2 minutes....due to the memory leakage thingy. So I had to wait 24 hours for new wu's...