Synchronized Combo Boxes not allowing Control Source data

[Heidi]

I have 2 combo boxes that are synch'd in a subform. The form tracks classes
and attendees. The subform holds the main combo where you can choose the
company name, the 2nd combo, the attendee name for the corresponding company.
The subform has 2 joined tables - a table called tblMain_Dtl, holding
(besides it's own autonumber) corresponding ID fields that links to the main
form by an ID and an MainDtl_Attendee_ID field that joins to the table that
is also part of the query for the form, tblAttendee. tblAttendee has the
autonumber, the Attendee_Name and Attendee_Company_ID that corresponds to the
ID in the tblCompany and the combo box for the company.

My problem is that the combos work fine as far as synch'ing but I want to
store the ID of the Attendee combo into the field that is contained in the
tblMain_Dtl (MainDtl_Attendee_ID) but no matter which way it is joined - beit
from tblAttendee to tblMain_Dtl or vice versa since it doesn't matter for
this form, I get this message:

The current field must match the join key 'Attendance_ID' in the table that
serves as the 'one' side of one-to-many relationship. Enter a record in the
'one' side table with the desired key value, and then make the entry with the
desired join key in the 'many-only' table.

Now if the company combo works fine and it is also joined tot he
tblAttendee, why is only the 2nd combo giving me issues? Any help would be
greatly appreciated.

Thanks
Heidi