Incorrect Mode: The meeting may still be in agenda mode. In order to create a follow-up meeting from a previous meeting, you must convert the previous meeting to minutes mode. See Convert a Meeting from Agenda to Meetings Mode.
Follow-up Maximum Number Reached: The maximum number of follow-up meetings that can be created on an individual meeting is 475. When the max number of follow-up meetings has been reached, users will receive a prompt alerting them to create a new meeting to hold subsequent follow-up meetings.