Just as a follow up my primary gfx card is an HD5870 but I also have an NV card installed (mostly for PhysX related things) however the drivers aren't completely up to date; could this becausing the above issues?
I don't see why it should as the OpenCL backends should really be working fine together...
1. Try restarting the system after a fresh driver install(10.8 or 10.7b) and run the samples.
2.Also try to run them in debug mode in VS2010 and quote the errors if any.
3.Only try the _86x64 samples as you are using x64 windows7.
Let me know the progress.