Can't Use Purchased Halo: Reach Defiant Map Pack

About an hour ago I decided to finally purchase the Halo: Reach Defiant Map Pack. After purchasing and downloading the map pack I started the game. After starting the game a message popped up saying that I needed to buy the extra content even though I just did. I've tried everything I can think of; I've dleted the installed game from my HDD, I've cleared the HDD cache, I've deleted the map pack and fully downloaded it a second time and nothing works. The game continuously tells me that I'm missing the map pack, but it's right there on my HDD, I can see it. Even when the game says I don't have it and asks if I want to download it and I click the "go to XboxLive Marketplace" option, it asks if I want to "download again", but the "play now" option is grayed out. Any help would be greatly appreciated as spending $10 dollars on something and not being able to use it is very annoying.