Facebook introduced API 2.0 on April 30, 2014 and forced all users to move to it. it brought some changes to the requirements for app and page ownership.
This means that the Facebook app, Facebook profile or page and the user who authorizes the app MUST belong to the same Facebook account. This Facebook account MUST be an admin for the page or member of the group where you are going to autopost.
Please see the full history of the issue here: https://www.nextscripts.com/known-issues/facebook-issues/