Warning: array_key_exists(): The first argument should be either a string or an integer in /home2/m

Warning: array_key_exists(): The first argument should be either a string or an integer in /home2/mno1/public_html/mnouniversity.com/wp-content/plugins/coursepress/includes/classes/class.course.php on line 374

what caused this and how do i or you fix it. units in course is not showing up also/.