If you have general Questions then read the FAQ

How can I play?
Download the .jar client and open it with Java.

Java must be installed on your system. You can find Java here.

Whats that: "You are already logged in!" ?
Only one player can be logged in with the same account. If this happens then open the Task Manager and close all processes with "javaw.exe".

Whats that: "login.xba" ?
This file is created after the successful login and contains your account data including password in encrypted form, so that you can log in to the account directly after starting with OK.