Good morning and thank you for posting on the Final Fantasy XIV Technical Support Forums.

This error indicates that your character is still logged in when you sign in. In your case, it seems as though the server has not recognized that you logged out (this is common if you are improperly disconnected from the game).

This usually resolves itself within 24 hours when the server acknowledges that you've logged out. Are you still having issues logging in?

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!