Some players that downloaded the Crimson Map Pack for Halo 4 have been reporting issues such as being perma-banned from Halo 4 Matchmaking.

Last week there were reports that the Halo 4 DLC had been put onto Xbox Live for free, players are unsure whether these bans are related to that event.

343 Industries said via the Halo Waypoint forum: "We are not permanently banning players for previewing or purchasing the Crimson Map Pack. We are currently investigating the recent reports of permanent matchmaking bans.”
"We will provide further updates tomorrow. Thank you for your patience."

We'll update you when 343 or Microsoft have announced the cause of these bans.