Help with nested subforms

[Stephan Ranocchia]

I'm having difficulties with the following setup:

Tables
Audit History (AH)
Audit Scope (AS)
Auditors (A)
AH_AS

Relationships
AH:AS M:M
AS:A M:M

I'd like to build a form bound to AH. Then within that, a subform that
contains AS (bound to a drop down) and that form contains another drop down
bound to (A).

Basically as users go through each record on AH, they can add as many audit
scopes as they'd like. And for each audit scope they can add as many
auditors as they'd like.

The table AH_AS has the following structure:
AHid
ASid PK
Aid PK

My form design is:
Main form (F1) has AH as it's record source. The subform (F2) is linked to
this form by AHid. It's record source is AH_AS. F2's also has a subform
(F3) and which is linked by Aid. F3's record source is also AH_AS.

This is obviously wrong because it's not working. On the AH_AS table I'm
getting records with either AHid set to 0 or Aid=0 depending on which drop
down I select. It seems to me that when I select a given Auditor for a
given Audit scope, the audit history id doesn't get carried over.

Can anyone shed some light on this?

Thanks,
SR