When you Generate the Academic Performance, check to see if you have 2 of the same Student's name listed with different grad years. For example:
John Smith '17 
John Smith '18

This usually means the user has 2 Alumni Affiliations which is causing the error to happen when saving as they are listed in both Grade Levels/Grad Years.

To fix this, navigate to:
  1. Core > Users
  2. Search for and click into the User's record
  3. Under System Information select Alumni Affiliation
  4. Click Edit on the Grad Year the User should not have listed
  5. Click Delete
  6. Click Confirm