This can happen if you create questions for the event but do not include them. When creating questions, you have to explicitly mark that the question should be included. To check this:
  1. Go to Content > Events
  2. Go to the "Event list" tab
  3. Click "Edit" next to the event in question
  4. Go to step 8, "Include Questions"
  5. Next to each question, make sure that the box is marked for "Include this question"