CoursePress Error - Viewing a Unit

Greetings.

When viewing a course unit on http://develop3.extremehosting.ca/courses/on-field-evaluation/units/the-safe-method/page/1/ I get the following error:

Warning: array_key_exists(): The first argument should be either a string or an integer in /apps/apache/web/develop3.extremehosting.ca/wp-content/plugins/coursepress/includes/classes/class.course.php on line 374

FYI...the site is hosted on and running PHP Version 5.5.30 on Linux and Apache 2.2