When adding a course recommendation the recommendation will not save.
You can not add Course Recommendations for a particular course if the student already has a course request for that course.
Remove the request and you can add the recommendation.
Steps to Duplicate
When logged in or impersonating a teacher: 1. Classes > Choose a class 2. Course Recommendations tab > Choose the appropriate Sign Up Period 3. Use the drop-down under New Recommendation beside appropriate student 4. See that it will not add