A number of players are apparently finding themselves banned from Halo 4 online play after purchasing the latest downloadable content. Microsoft has acknowledged the issue and is currently investigating.
"We are not permanently banning players for previewing or purchasing the Crimson Map Pack," confirmed a 343 Industries forum moderator. "We are currently investigating the recent reports of permanent matchmaking bans."
There's an official ban thread on the studio's message board, which should update with further information on the subject.
What is it with Halo and bans? That series seems to attract these incidents like Calamity James and hilariously labelled falling weights. That Beano reference has absolutely no resonance here.