Is NordersDetails the name of the control that houses the subform, or just the name of the form as it appears in the Forms section of the Database window? Use the steps I mentioned above about NameOfFormControl to verify it. If the control is named NordersDetails, and that subform has a textbox similarly named ProductId, then you would use:
[VBA]
Forms!NordersMaken.NordersDetails!ProductId = Me.ProductId
[/VBA]

If that still doesn't work, let me know. I'll have something experimental to try.