I was just pulling my hair out for a few minutes because all of my cards were showing the dreaded "verification failed, check hardware" on the command line interface after just a few seconds of mining.
Thank goodness grinder made this post here: http://bitcointalk.org/index.php?topic=1334.msg97772#msg97772
I added -v (vectors) to my poclbm variables and it began to generate flawlessly. Going on 20 minutes now with no "verification failed" messages (fingers crossed!).
Can anybody explain to me what exactly "vectors" are? Am I still using the BFI_INT calculations with vectors on? (I am using the latest POCLBM version which I believe calculates BFI_INT now as well?)
With vectors enabled each thread on the GPU runs 2 hashes instead of 1. This improves performance on ATI hardware because it gives the compiler more opportunities to extract ILP (Instruction-level parallelism) compared with only running a single hash.
The latest poclbm always uses BFI_INT on ATI/AMD hardware if cl_amd_media_ops is detected. I am not sure why enabling vectors can "fix" the problem when all it does is run 2 hashes per thread on the GPU instead of 1. This may be a problem with poclbm's BFI_INT patcher, which I haven't looked at in detail yet. I don't think the OpenCL kernel itself is the problem because as m0mchil mentioned it is virtually identical to the OpenCL kernel used in Phoenix now. I have yet to see any users have this problem without vectors on Phoenix though, which is why I suspect the BFI_INT patching code.
That said, vectors should be faster on most ATI hardware anyway, so this shouldn't be a problem for the majority of users.