When the Modern Warfare 2 "Stimulus Pack" downloadable content launched, it did not work. Surely there had to be a reason for that. Turns out, there is.
Issues included: Multiplayer lobbies not working, images for maps not showing up and no option to play private matches. According to Xbox LIVE Operations Manager Eric Neustadter, the broken launch was the result of a "process failure".
The Stimulus Package was released on March 30, before the Title Update for Modern Warefare 2 became available. Thus, the DLC would not work properly. "For a couple of hours the result was unpredictable but most people couldn't get into a game through matchmaking," Neustadter recounted in the Xbox Live Operations Blog. "In technical terms, it was a big hairball that we had to unwind."
Xbox Live Operations Blog : Today's Xbox LIVE issues – Modern Warfare 2, Matchmaking, and Billing. [Xbox Live Operations Blog via Eurogamer]