Sorry for not clarifying... yes, these two fields are PF/PK dependent.
> Tbl_CBillTo.CUSTNO (PK) links to Tbl_SOHeader.SO_CUSTNOREF (FK)
> Tbl_SOHeader.SalesOrderID (PK)
To further clarify my scenario, I'm basically opening up the form to a new record, assigning the PK (SalesOrderID) and then...