phpcalendar install script generates error message

I have just now installed phpcalendar using VMPro. On accessing the app I get a working installation with an error message at the top of every page saying:
“Notice: Undefined index: HTTPS in /home/choked/public_html/phpcalendar/includes/setup.php on line 28”

Line 28 seems to be where the script is figuring whether there is a secure session (http vs https). Anyone else seeing this? Ideas about what to do?