Could be a couple of things.
1) Try turning off any preload options in the game's "Video Settings", then try and connect.
2) Could be a port being blocked by your ISP, local firewall, or router. Some ISP's actually block specific ports that happen to be ones we use. They claim it is an effort to block P2P clients.
If you can connect to the Orange, or Allied versus Axis arenas, then I would say it is probably #2 as those other arenas are on the same server, just different ports.