The enrollment attribute configuration for the Sponsor or Manager enrollment attributes allows for a default value. When fewer than 51 People are available to list, the form will default to a dropdown (select) box. In this circumstance, if the form receives no records, instead of displaying an empty dropdown box, provide a message to the user explaining that there are no available sponsors (or similar).

There also may be cases in which fewer than 50 records are available for Manager or Sponsor, but the People Picker is (incorrectly) rendered. Investigate (probably starting with the return value of sponsorList() in CoPerson.php).