Default value "the previous value +1"

[RuralGuy]

That should not have compiled. No '=' required.

Private Sub Customer_No_BeforeUpdate(Cancel As Integer)
   If Me.NewRecord Then
      [Customer_No] = DMax("[Customer_No]", "Customers") + 1
   End If
End Sub

 

[boblarson]

Actually that is in the wrong spot. It should be in the FORM_BeforeUpdate event NOT the CONTROL BeforeUpdate. That is your problem as it isn't adding the number in like it should.

 

[RuralGuy]

Good catch Bob. Duh!