I purchased the war games pass the same day halo 4 came out at Gamestop for 24.99. I redeemed all my codes I got in my receipt including the war games pass code. When the crimson map pack came out I downloaded them. I was able to play the map until this past week where i have not been able to play the maps. I called Gamestop to see if there was anything they could do. They were not able to help but told me to get in contact with Microsoft that they can help me. I than called Microsoft and spoke with a represenative for about an hour and we tried every troubleshooting they could offer but could not resolve my problem.
Go to the Settings tab on the dashboard. Choose the “Account” tile. Select “Download History”. If you redeemed the War Games Map Pass, it should appear in the list, and the license key can be downloaded again by selecting it.