Resolution: Delete the App from your Apps you use page. Then hit Grant Access again and the dialog will start and you can reactivate the app.
Facebook returned an unexpected dataset. Try to resolve this issue, update the plugin or inform the author about the problem.
[Error occured at line 601]
Your application's access permissions could not be granted.
Some or all access permissions are missing. Please click the button Grant access rights! and authorize the plugin to post to your Facebook profile or page.
[Error occured at line 778]
Your page or profile's access permissions could not be verified.