Members Directory Plug In

I have purchased Members Directory. I installed that plug-in as well as the mandatory free WPMU DEV Dashboard Plugin. In my Dashboard there is a horizontal line going across my screen that says: Fatal Error Call to undefined function is_site_admin() in /home/content/08/914508/html/wp-content/plugins/members-directory/members-directory.php on line 58. Please can you help with this as we are launching our website tomorrow morning and this was the last thing for us to do. eddietables

Furthermore, all of our additional plugins are updated with no problem as well as WordPress to the newest version. Now I can not see the Menu section under Appearance. Please help.