CoursePress Pro

Hi there,

I am new to Course Pro and just finished my first Unit. When push preview, non of the course material appears and there is a warning:

Warning: array_key_exists(): The first argument should be either a string or an integer in /home/geldkatz/public_html/wp-content/plugins/coursepress/includes/classes/class.course.php on line 374

Thanks for your help!