It seems like memory corruption, the most annoying kind of bug. Might take some time to fix, I haven't been able to reproduce it on my computer.
This is a serious problem that may not have a fix. I have a GPU that I still have running on SHA256 because it starts throwing massive errors if I try to use the same intensity on scrypt coins. 300MH vs 174KH running 16 vs 11 intensity. Many of these GPUs have been running on hyperdrive for months on end, but until now they have not had to deal with the intensive memory load that your miner is throwing at them. I'd bet your program hits GPU the same way P95 hits CPU... it stresses them to the point of failure not seen in normal/somewhat heavy operation. With all the underclocking/overclocking/undervolting/overvolting I'd bet there are a lot of cards that appear to work fine yet are hiding a major problem.
Memtest is a fairly intensive memory testing program, but it's not as intensive as P95. I've seen many posts about people saying the P95 program was faulty cause it crashed their computer yet memtest said no problems. Not once have those claims been proven out though, it's always ended up that P95 stressed something harder than memtest and found a problem that needed fixing.
I vaguely remember someone on the Mersenne forums having written a crude GPU program to simulate what memtest does... maybe you need to have people start looking into that.
Until then, I'd suggest you start having people answer a few basic questions to start the troubleshooting...
1) How old is your GPU?
2) Have you ever OC'd or declocked it?
3) What intensity settings have you run it at on other coins and for how long?
4) Have you ever over/under volted it?
I'd be willing to bet the answers to these 4 questions will start a pattern for those who have it working and those that don't.
1, About one to two months old.
2, yes slightly both ways, but it runs so hot that I most often let it run on default.
3, I usually use 10-15, I haven't been running any mining application 24/7, just a couple of hours to try the cards out.
4, Yes but not through any manual process, I have only used the built in +-20% voltage.
//DeaDTerra