Error after selecting the Certificate tab, once completing a quiz.

Using Drupal: 7.23, Quiz: 7.x-4.0-beta1. I'm logged in as the admin user, no other users in the database. I've set up a simple certificate, and a quiz with the certificate assigned. Nothing fancy or unusual. When I complete the quiz the certificate tab is visible. Clicking on the Certificate tab yields white screen error:

Fatal error: Call to undefined function profile2_load_by_user() [my site]/sites/all/modules/certificate/certificate.module on line 751

Any help is appreciated and thank you in advance.