Restart Steam a few times. If that doesn't fix it, close Steam, delete clientregistry.blob, and restart Steam. If that doesn't fix it, change your download region and restart Steam.Bought MW3 on Steam and after spending hours downloading it says Error The Steam servers are too busy to handle your request. Error 55. What the hell does that mean? What do I do?
For all I know, none of those things may have any effect, but it will make you feel like you're doing something, and maybe it will work by the time you finish trying them all. I am not a fan of the error that prevents one from launching single-player games, especially.