We are aware that after today's unscheduled maintenance, some players are still experiencing server instability and disconnection issues. These issues include players not being able to select a world in the world selection screen, and "ID is already logged in" errors.
We are currently investigating these issues and will provide updates as soon as we have them.
Again, we apologize for any inconvenience this is causing. Thanks for your patience.
-The MapleStory Team