This is caused by a mismatch in the Core Student User ID and the School Student ID in Smart Tuition.  We know that Core User IDs can not be edited, so this must be corrected in Smart Tuition so the ID numbers match once more.

In order to correct the School Student ID in Smart:
  1. Search for the School by ID and select the correct year
  2. From the Families dropdown, select View All Students
  3. Search for the student and click on their name
  4. Expand the left sidebar menu and select Update Parent and Student Info under More Options
  5. Edit the School Student ID under the correct student name
  6. Click Save Changes at the bottom of the page