Thanks for replying Tim.
I have run the database check as per the instruction in the link. The database is clean with no corruption.
Let's be specific about what I see:
Teacher creates Feedback
Student logs in, enrols in course
Student clicks on Feedback and is shown the editing screen - as a result is unable to complete the Feedback (this happens for all "students" not just one of them.)
I login as an admin, go to Users, Assign System Roles, See the student in as a Course Creator, delete them from that list, Click on Assign System Roles, Logout, log back in again and that user is still a course creator.
I have also thought that there may be a newer version of the Feedback Module - but as it will be core in 2.0 the ability to download the Feedback Module has been removed.
Any suggestions appreciated.