Sounds like a weird glitch man, try deleting your most recent update and re downloading? If that doesn't work i would suggest re installing your map pack. Sucks but that sounds like a crappy bug or corrupted data.
This is a great suggestion.
sdfffr, please go ahead and do that, here's how: http://support.xbox.com/en-US/xbox-360/settings-and-initial-setup/clear-system-cache
If your DLC is on an external device, please remove all of it and redownload it.
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