I've figured out what causes the problems joining games, and have a solution to prevent you from getting the error. The problem is that when people play, and then quit, the server still lists them in the game because it has to keep track of their stats, but in the server list, just lists the number of players connected o the server. When it has a full list of stats to keep, then there is no space for new players to join, even though the room isn't full. The solution to the problem is to join games with lots of time remaining. I garuntee that 9 times out of 10 if you try joining a game with full time remaining then you will get in.