I've downloaded the Crysis 2 demo through Stream, but when I try to run it I immediately get the error message

Failed to initialize the GameStartup Interface!

and nothing happens after clicking the "OK" button. What causes this problem, and how can I fix it?

System specifications:

• Windows 7 64bit.
• Nvidia Geforce 250 GTS, with latest drivers.
• All other PC stats also matching or exceeding minimum requirements as specified in the Steam Store page.