Q: Okay, I gave you my hard earned monies in exchange for one brand spankin' new Defiant Map Pack, but after successfully downloading and installing it, none of the maps show up in the game menu. What gives?
A: Turns out that there's currently a technical issue tied to the number of Marketplace Content items you can have active for Halo: Reach at any one given time (this does not include Saved Games, Screenshots, or Saved Films). Right now, you can only have a total of three content items simultaneously active. Items that fit the bill include pre-order bonus or retailer exclusive armor, map packs, or your Bungie Pro confirmation.
Microsoft is working on a long-term solution, but for now, you'll need to delete one of the three items you have active. Here's how you do it:
In your Xbox 360 Dashboard, sign into your profile, and navigate to the System Settings tile in the My Xbox list. From the settings pane, select Memory.
Select Hard Drive as the storage device.
Select Halo: Reach.
Select the Bungie Pro Confirmation Marketplace Content item.
Deleting the Bungie Pro confirmation item will not impact your Bungie Pro Membership in any way.