A handful of gamers are reporting that a manufacturer error has caused some of the second discs in copies of Black Ops 2 to be replaced with the second disc for Mass Effect 2. So far this has only been a reported issue with the PC version of the game. The disc is clearly labeled as Black Ops 2, but upon inserting the disc into your PC you find that it is actually ME2.
Using the Steam code for the game resolves this issue, but it sucks for people who don’t have a good internet connection. Once you use the Steam key, the game can be downloaded using your account.