Disconnections usually occur when: 1. The server undergoes an automatic restart. Try to log back in after 5-10 minutes.
2. The administrator is running a manual restart. The thing here is that you don't log back in until the administrator gives the signal. How do you get notified? Checking the chat-room helps. Sometimes, the administrators are not present there (they're busy on another computer) and so you'll have to wait it out.