im getting a error message when updating profile for the service providers

Hello WPMU hope your day is great for every day you are in my life i worry alil less about my WordPress sites...for i am not a hard coder... or even read much of the language.. and that is were i turn to you for help

i am having a problem with the appointment plugin... every time i try to update the service providers details on Users page, under "Appointments +: Personal Data" section I get:

Notice: Use of undefined constant CTX_STAFF - assumed 'CTX_STAFF' in /home/jjswestvalleyac/public_html/wp-content/plugins/appointments/admin/class-app-admin-user-profile.php on line 20

Warning: Cannot modify header information - headers already sent by (output started at /home/jjswestvalleyac/public_html/wp-content/plugins/appointments/admin/class-app-admin-user-profile.php:20) in /home/jjswestvalleyac/public_html/wp-includes/pluggable.php on line 1171

can some on please help me understand this code why i am getting this error... and wave your magic wond and fix it for me for i have granted support access to the site... please