I have the same problem on the xbox 360 , bought season pass downloaded Devastation map , cant download Onslaught ,
told by Activision support it may be because i have a wireless connection , (crap) it doesn't stop me downloading anything else,
including deleting and reinstalling the Devastation map pack, same size 1,2 gig , dodgy season pass code. ripp-off as long as they get their money . the excuses keep coming.