Does the marketplace allow you to download the map packs again? If so (you will probably have to pay for them again) download again and see if it works. If not key in the "x,x,right bumper,left bumper" code when you go to sytem/memory/and press Y on the HD (hard drive) option. If you have not done that before, all it is, is system maintenance and it will clear the 360's hard drive cache and delete updates and such. You will have to re-update your games but it might help you do re-download a map pack that has been downloaded on someone elses xbox. This probably won't work but it's worth a try.