While it looks like most of these errors on linux are caused by registration/path issues, my problem turned out to be different, so I thought I'd share my fix.
I'm mining on a brand new Ubuntu Natty Narwhal install, and after completing installation here (http://forum.bitcoin.org/index.php?topic=7514.0
) with SDK 2.1 I kept getting the "FATAL kernel error: Failed to load OpenCL kernel!" error. None of the usual solutions helped (re-registering the SDK, resetting the library path, etc.).
Turns out it was the command line I was running:
./phoenix.py -u (1234)i:email@example.com:8337 -k poclbm DEVICE=0 VECTORS
BFI_INT FASTLOOP AGGRESSION=6
After dropping 'vectors' off my command line, mining works fine.