You can only get to the online course registration page by using the course calendar or course schedule page. Unless you know the course ID, you can't get to it. Added a check if the course date is before the current date on the online course registration page.

if course_instance.course_date_from < datetime.datetime.now():
    return render_to_response("sorry_course_unavailable.html", {"course_code": course_instance.course_code}, context_instance=RequestContext(request))