GTX 970 under OS X 10.10.x and all updated NVIDIA drivers produces this error:
cuCtxCreate: invalid source
The problem is that current CUDA is NOT compatible with the NVIDIA GPU web drivers.
To make use of CUDA use an older version of CUDA.
GPU driver: 343.01.02f03 till 343.02.01f01
CUDA driver: 6.5.25 Nothing after will work currently - Dec 26)