Can't update data from query based form (1 Viewer)

Hi, - I'm a bit flummoxed as I edit table data in query based forms all the time, but I just seem to have hit a brick wall. I'm guessing the way ive got the tables set up is not really very good, but I've done much worse and been able to edit table data through a form based query. I included a cut down sample of what i'm doing to illustrate a point. Briefly, the current app/database is to join a table of students who have Special Requirements (SR) for exams to the data extracted from the main uni SITS database of modules, so I can join the student's 'SPR Code' on each, and grab module info from the SR students who have a match in the 'Module Taking' table. I can then add new and edit existing students, adding to their SR needs, adding notes to the record etc. But the form is just fully locked as soon as I have more than one table in the underlying query, fine if just one (i.e. straight to the table). I can get round this by selecting Dynaset Inconsistent Updates, but I don't know what sort of trouble i'm storing up for later in its devt, plus I've not had to do it before.

I include the database, as it's probably easier to see what's happening directly, and I've given clues in the form and query names. Does anything look obvious to you? I must reiterate that over the last 15 or so databases I seem to have not had the problem, even with back ends I know are quite messy, but have not had time to revisit and tidy.

Well, I say I include the database, having the odd problem.......

**Thanks for your replies up to now; I did finally manage to get back to where i'd saved the )(shortened) db.....

db missing?
you might find this helpful
http://allenbrowne.com/ser-61.html