Actually you can prevent it and if the server was full it would tell you but I doubt that's the case since it can hold hundreds of users.
Anyway, snapeboy if you have a firewall on then that's probably whats not allowing you to connect to the chat. Another posibility is a router that's blocking you. You'll need to open port 6667.
EDIT: There was a minor network problem, which is fixed now. A new server that isn't configured yet was added to the round robin and didnt accept connections. Don't worry if you didn't get what I just said, the chat is fixed