GPU Acceleration disabled because of an Error!?!?!

Hey everybody, 

I've an Geforce GTX 980 Ti and sonce a few weeks the GPU Acceleration isn't working properly. Everytime I use the Crop tool, LR freezes for a few seconds and then the new Preview wouldn't be rendered. When I go to settings, there's a Message unter the GPU Setting that says "GPU Acceleration disabled because of an Error".

Any advice or tips? to get it working again? Disabled GPU is slowing down a few thing pretty hard.. so that would not be the best way to fix this!

regards,

Manuel