For those having woes with the latest DLC pack for Modern Warfare 2 on Xbox 360, everything has been cleared up and Microsoft has released information detailing what the problem has been.
According to the Xbox Live Operations Blog, there was a 'process failure' on the Xbox Live side of the update. This consisted of the map packs being released before a title update that let players actually use the maps, which wreaked havoc on the matchmaking systems over Xbox Live for Modern Warfare 2.
There were also apparently a few issues with activation cards as well, but the blog is reporting that that issue should be solved by now as well, since there was just a backup of activation confirmation from vendors. Good thing everything is back up and running, now everyone can got get their stimulus fix that they have probably been craving for a while now.
Source: Xbox Live Operations Blog