Membership plugin not working after update to wp 3.6

I just upgraded to WP 3.6. Before upgrade plugin was working fine. Now if you are not logged in as Membership Admin you cannot access any part of the site front end (all shows as protected).

Also, non admins get this warning in their dashboard (but admins do not?)

Warning: Cannot modify header information - headers already sent by (output started at /home/content/59/11034659/html/wp-admin/includes/template.php:1706) in /home/content/59/11034659/html/wp-includes/pluggable.php on line 875

It is imperative that this get fixed ASAP! Marketing for this site just went out - HELP!