We have just provided a new update which fixes a problem that prevented the game starting on some machines (displaying error code 3). It seems to be due to a registry entry not being found, and was related to our recent removal of the 3rd party keys. Apologies to those affected and we hope this is now resolved. Please allow the game to auto-update from the Steam console and try again.
[We have had feedback from customers to confirm this is now fixed]