If you are using nvidia drivers be aware that nvidia deprecated support for HQ and VP2 rendering on all geforce cards. You will have to roll back to rev 158 of less to get the functionality back. I had to roll back to 157.21.

Nvidia says it was an accident but adds geforce cards are not supported for use with maya. I find it interesting that they break support for maya in the geforce line at the same time they announce a new batch of quadro cards. I smell marketing poo poo.