I have the same card and am getting the same error only with L4D. At first I thought the driver update didn't take. But as you can see with GPU Z.
Everything is fine. Says 9.4 right after 18.104.22.1685. So you are updated. L4D is just wrong.
P.S. I really wish the driver date and version in the device manager matched the date and number on driver update pages.