You probably should post this on the divinity forum on Steam so that their admin is at least aware in the event that this issue occurs for other people.

http://forums.steampowered.com/forums/forumdisplay.php?s=4c1bc2b0f3293f9724399808a3cf0b27&f=822

I would also try either validating the game from within Steam or deleting the local content, and uninstalling your Physx driver and try installing Div 2 from Steam and letting it install the Physx driver.