Have you excitedly purchased the Halo: Reach Defiant Map Pack only to find that it's not working properly? Some of you might find that you're unable to access the three new maps, which is down to a technical issue that allows you to access only a limited number of Marketplace items for Halo: Reach at once.
"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)," reads a post on the Bungie.net Blog addressing the issue.
"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."
This means that you'll need to head into your Xbox 360's Memory menu and delete one of these items while Microsoft beavers away on a long-term solution. Bungie suggests deleting the 'Bungie Pro Confirmation Marketplace Content' item, as this won't affect your Bungie Pro membership in any way, and will free up the slot necessary for the Defiant Map Pack.
Have a closer look at the Bungie.net Blog if you're still experiencing issues.