This error happens when your Facebook tokens have been invalidated — usually by a changed password.
Common Error 200 Messages
Error validating access token: The session has been invalidated because the user changed their password or Facebook has changed the session for security reasons
Error validating access token: The user is enrolled in a blocking, logged-in checkpoint
The fix here is a quick one!
Just head to Settings > Social Networks and click the "Refresh" button on the Facebook row.
If the problem persists, do a full app reset.