A number of Forza 4 players are reporting on the official Turn 10 Forza 4 game forums that they have been banned from playing the game without so much as a valid reason.
While not admitting there is a problem, Turn 10 is looking into these reports to see if the banning reports are valid. Apparently, the problems center on the auction house and buying and paying for cars with real world money.
Turn 10 says that they take reports like this very seriously and that they will get to the bottom of it. If necessary, accounts banned in error will be reinstated. We will just have to wait and see what happens.