[Resolved] Known Issue - Not A Registered ID Error

http://maplestory.nexon.net/news/news/current/00IQa/

Dear Maplers,

The Nexon accounts created after April 1st, 2015 are receiving an error which states "This is not a registered ID." Afterwards, the game client will shut down. We are currently working to resolve this issue.

We apologize for the inconvenience and thank you for your patience and understanding.