Nvidia 3d vision not activating automatically

In theory, since 3d vision enabled games render twice as many frames (one for each eye, rather than just one for both eyes) you would expect the framerate to be roughly 50% of normal.

However, according to this, the Nvidia Fermi architecture (4xx and onwards) seems to have improved on this which reduces the performance loss to only 38%. I would expect this to vary depending on your hardware configuration and the particular game since different 3d engines stress different aspects of your hardware (CPU, fill rate, GPU memory bandwidth, etc.).

In your case, the GPU your are considering is mid-range so I would expect a significant performance loss when enabling 3d vision on modern games.

I "found" the "solution".

Update to 304.79 BETA drivers then it works again. It was just a driver issue.