LinkMasterField stopped working

[PeakH]

I have an invoice form that includes a master form (OrderID, Customer, SaleDate) and a subform (Product, Price, etc.). The forms are linked on OrderID, and were working correctly until recently. I'm not sure what I did, but now when I try to enter a record in the subform I get a notification "The LinkMasterFields property setting has produced this error: 'Expected: =' "
The Link Master Field and Link Child Field are set to the proper fields, and again this was working as it should just earlier today. I tried uploading the database to onedrive so that I could share it with my co-workers. Could that have done something?
I even tried creating new subforms, replacing the old subforms and re-linking them. Still I get the same notification. Now the records are saved to the subform table but with no OrderID, so if I try to open an order on the form, no products are linked to it the way they ought to be.

[ranman256]

The parent (master) form record MUST be saved first, before any subForm records are entered.
you may want to disable the subForm until the parent rec is saved.