Try each of the following steps in order until the error is resolved:

1. Ensure the grade level is not present on records:

     a. Create a new student query.
     b. Filter on Current Grade equals [grade level] OR Student Progression Grade Level equals [grade level].
     c Place the desired fields in the Output and Sort.
     d. Go to the Results tab to view the selected records.
     e. Either remove or change the grade level on the record.
     f. Delete the grade level from the school.

2. Ensure the grade level is not marked on a course record:

     a. Create a new course query.
     b. On the criteria tab, select Restrictions 1, Grade levels allowed.
     c. Set this equal to the grade level to be deleted.
     d. Open these course records and unmark the grade levels.