Mercury Playback on Cuda

Hi,

I have the trial version of Premiere Pro CS6 (I just updated it today) on Windows 8 with 2 Nvida GTX 680 SLI graphic cards.

When I try to activate "GPU Mercury Playback Engine (CUDA)" the videos are all black. I can still read the videos, but I have only sound and no image.

Could someone help me?

Thanks for helping