I'm not seeing much else for this issue, is there anything else to the error message that it gives you other than "Game.App can't be opened"? And do you know what version of Mac you are running? The only other thing I've seen is to go into your "System Preferences > Security & Privacy" settings and in the "General" tab, there's an option you can select to allow apps downloaded from anywhere to open. That might not be the best solution as it makes your computer more vulnerable to other programs, but it's worth a shot I suppose.