Apple Mac GPUs always hang on Cycles render start AMD ATI 6750M I have an iMac and want to use my GPU.

Everytime i want to start the Rendering with cycles, it's written to wait a view minutes till the kernel will be loaded, and than my mac creshes and i have to restart.

i Searched and the AMD 6750M seems compatible with Blender 2.79b, but it don't works.
Thanks a lot, on my second Mac the same thing. When I set up Cycles and start the rendering Che System Preference panel crashes, and blender creashes to :(