I'm experiencing this identical problem. Did anyone ever find a solution? The odd thing is I didn't have a problem with a questionnaire I created about a month ago. We are running Moodle 1.9.7 and Questionnaire Version 2008060402.
Recently we changed permissions on our moodledata directory, and I'm wondering if it needs certain permissions for this to work?
Thanks for any advice you can offer!
Sallie