Problem

Cannot change the Evaluation Group originally assigned to my Questionnaire

Cause

If at least 2 questions have been assigned to different evaluation groups, you cannot update the assignment under Criteria. 

Solution

You can overwrite the assignment under the Questionnaire tab instead. To do so, select the Questionnaire you wish to re-assign, and select Edit:

From the Questionnaire, select the Questions you wish to re-assign and select Bulk Edit:

Select Change Evaluation Group and choose the Evaluation Group from the List: