Part of the course has not been completed
If the course is taught in several semesters, its syllabuses are presented in parts (part 1, part 2 etc). A precondition for registration for the following part may be completion of the previous part(s).
The text is displayed: Part X of the course is not completed.
At registration for courses, there is no active checkbox in front of the course title, and there is a text informing about the restriction (see Figure).
If you have added the course into the planner, and it has a restriction for registration, an exclamation mark is shown next to the checkbox, and when moving the cursor to it, you can see an explanation about the restriction (see Figure). Registration for the course is not possible. By filling the checkbox, you can remove the course from the planner.