Well if its freezing for that game only, its possible whatever the save is it wants to load, is corrupt, so I would move all BO2 files to a separate drive, remove that drive(USB) and then delete all saves from the XB HDD. It's usually associated with the most recent save, as that would be the one its trying to auto load. Now, if you don't have a lot of progress done in the game before it started freezing, then backing up the files may not be too much of a concern for you. I just didn't want you to lose all data which is why I suggest moving a copy of the saves off the console.
Once you delete the saves, try loading the game and seeing if it still freezes, if it doesn't, bring back the saves you copied off the HDD, starting with the oldest file, 1 at a time. After each file, try loading the game again, if it was a save, eventually one of those saves will cause it to freeze again, and then you know which one is corrupt.