This can occur if the 'Parents are' field has been use on the application and only one parent is matched within The Education Edge plug-in.
Verify that both parents are matched within the plug-in.  
 
  1. Click on view relationship matches
  2. Verify both parents are matched. If not, highlight unmatched parent. Click Add a match.  
  3. Search for Parent, and then link appropriately.
  4. Process form now.