I got discoed again today it appears it is happening when the arena fills up and somebody else logs in it kicks somebody off to make room.  When I got discoed I immediately tried to get back in and the areana was full.   This makes 5 times this month that this has happened and each time when I get back on the arena is full each time, so it must be something with the server doing it.  my ping runs 78-110 on AT&T/.