Submissions for a questionnaire created from a node are not showing.

After adding a submission to a questionnaire created from a node, when a user tries to edit the submission, the following exception is thrown:

Notice: Undefined index: questionnaire_question_submission_form in drupal_retrieve_form() (line 806 of /var/www/html/TestSiteThree/includes/form.inc).
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'questionnaire_question_submission_form' not found or invalid function name in drupal_retrieve_form() (line 841 of /var/www/html/TestSiteThree/includes/form.inc).