Error on profile page members-only.php on line 131

All working fine with the plugin

However when you go to a user profile just above the feed key this error shows

Warning: Use of undefined constant permalink_structure – assumed ‘permalink_structure’ (this will throw an Error in a future version of PHP) in /var/sites/w/worldwariipodcast.net/public_html/members/wp-content/plugins/members-only/members-only.php on line 131

The page I need help with: [log in to see the link]