Well this is a little embarrassing, some players who purchased the PC retail version of Call of Duty: Black Ops 2 have discovered that disc 2 is actually a copy of EA and BioWare’s Mass Effect 2.
Players on Reddit, the Steam Forum, and the Call of Duty forums have all reported the issue and claim that it is impossible to complete the game’s installation as a result. The exact cause of the error is unknown, but it’s likely that something went wrong during printing.
There is a way around the issue luckily, all you have to do is add a game via steam and input the serial code on the box and the full game will begin downloading.