Course Instructor's Can't "Manage Course"

My Course Instructors can no longer manage their course. When they click on the "Manage Course" button, they get the following error message:

"Cannot load course_details."

But, when they go directly to "wp-admin" they can access their course area. Already tried "debug" mode, no error was present. Already tried deactivating certain plugins also, that did not work. Issue has been present for at least 1 week. Cause is unknown. Access has already been granted in case you want to take a look.