GFWL saying I have already used my key but I havent?! (Just got Halo 2 for Windows Vista literally 3 hours ago, had trouble installing it and now this?!?!) It says this exactly: "Can't sign in because your product key is not valid. Please enter a valid product key.". I just bought this game off of amazon last night, so it wasn't torrented or anything.
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Yeah I had the same problem too. For some reason each time I enter the code that message shows up. My copy is brand new too with xbox live gold.