Hi there,

Bad news! The participant 

  '{{ user }}' in the course '{{ course.identifier }}'

just encountered a situation where his/her session contained page set-up
information for the page

  {{ page_data.group_id }}/{{ page_data.page_id }}

within the flow

  {{ page_data.flow_session.flow_id }}

that was out of sync with the current course content. Perhaps you have
non-sticky versioning enabled and have added or removed pages to the flow. (You
shouldn't have, see the docs.) The participant was instructed to contact you
for help. One possible recovery is to enable sticky versioning for the flow,
another is to delete their flow session (and lose all their input so far in
this flow).

- CourseFlow staff
