If you are having trouble after downloading the latest Call of Duty: MW3 DLC Content Collection 4 pack for Xbox 360 here is a workaround to launch the game with all owned content:
1. Go to Settings
2. Select System Settings
3. Select Storage
4. Select Hard Drive > Games & Apps > MW3
5. DELETE one of the 56 KB files titled "Collection 1/2/3/4 - Marketplace Content"
Outlined in this photo:
Please contact ATVI Support if you require further assistance:
We'll have a TU released that will fix this issue for everyone, but for now this work around will not cause you a content loss.