The recieved string length is longer...

Whenever anyone tries to log into the server they get the message "The recieved string length is longer than maximum allowed (23>16)" I have no idea what is causing this and ive waited a day and nothing has changed, the control(run thingy) shows no problems on start up and no problems when someone logs in, it just says the player has joined and than the player has disconnected, i dont really know any info i need to give out, but just reply what you need to help and ill do it