Getting a form to add data to tables

[Lucas Rhodes]

Hi all. I have a many to many relationship between two
tables in my database, and I made a junction table to
link them. I'm an access newb in the process of teaching
myself. So far I've been entering data directly into
tables but I'm trying to get beyond that and use forms.
The two tables are "court cases" and "defendants." The
reason that it is a many to many is because, while
unusual, there will be times when a defendant is involved
in more than one case.
I used the form wizard to create a court case form,
with a defendant subform. I have no problem entering
court case info in the main form, but I get an error
message popup "field cannot be updated" when I enter
defendant info into the defendant section of the main
form. I can then close the error window and then continue
entering data on the defendant. Each time I start on a
new record for a new defendant, the error message repeats.
If the form allows me to enter defendant info, why do I
get this error message with each new record?
So far the database is only on one computer and I'm
currently the only user. "Help" just said that someone
else has the table open so I can't update it. This
obviously isn't true.

Here are some (hopefully) relevant property settings.
These are identical in both main and sub forms.

under data tab in properties window: allow edits,
deletions, additions, data entry, all set to yes. record
locks, set to no locks.

Also, the form does not update the junction table, when
I add new case records and their defendant records.
Anyone have an idea why?

Thanks a lot for any advice you folks can give.

-Luke