Mark, I want to make sure that I understand what you are trying to do. I created a UDF in SO_InvoiceHeader called BILL_TO_COUNTRY source of Business Object, Business Object = SO_Invoice_bus, Data Source = BillToCountryCode, Column = CountryName. I then added this UDF to SO Invoice Header. It populates the UDF based on the Bill to Country on the address tab of the invoice. I am not sure if this is what you are trying to do, but if it is I was able to do it.