Take a look at this website:
http://maple-server.com/login.php

Their private server could solve the "ID already logged in" problem. Could ours too? Because today, June 1st, I was playing while i disconnected and i tried LOTS of times but i always get tat error... Could you help?

IGN: RaCiNgTeArS

Well, it might be hard to because the source might be different. Or maybe they invented that themselves.