I thought about that... essentially using the Customer table to bind the main form to, right?
I didn't try it because I didn't see how it would avoid this error, unless I'm picturing the cause of the error incorrectly:
When a user inputs a PO number, the Customer Name still isn't selected, and I'd still get the error, correct?
Or are you suggesting this to attempt to force them to select (or input) the Customer Name first?
It's not bad logic from a database integrity standpoint... mulling over "user friendliness".
Primarily what I don't like also about the subform is that if I select a customer, then my subform will suddenly contain a dump of all the PO's for that customer... and they'd have to scroll waaaaay down to the bottom to input a new one. Or, if I forced it somehow to be an input-only form, then I remove their ability to update (should a date change, for example).
It's such a simple form, that's why this seems so complex:
Customer Name (really CustID behind the scenes)
PO Delivery Date
Assembly Part Number
Assembly Revision Number