I get the error:
"Unable to load c:\program files\steam\steamapps\[username]\[game]\bin\filesystem_steam.dll" or
"CFileSystem_Steam::Init() failed: failed to find steam interface"
when trying to launch a game.
Please see the Verifying GCF Cache Files article for instructions to repair your game cache files.
PC Tools Spyware Doctor is known to cause this issue. Please see Programs Which May Interfere with Steam for more information on resolving this issue.