The game just bans at some times, if you let that ban pass and then try to join again you will most likely be able to play untill the next time it happens, and it can pretty much come and go as it please.
The game doesn't really ban you just because you have a mac, more because of the way mac connects to the server, this can cause problems at times.
Try to play once the ban has passed, it usually works for the others.
