Current event of main form:
If IsError(Me.totUnits) Then
Me.AllowAdditions = False
Else
Me.AllowAdditions = (Nz(Me.[COLOR=red]NameOfSubformControl[/COLOR].Form.totUnits, 0) <> 0)
End If
After Update event of subform:
Me.Parent.AllowAdditions = (Nz(Me.totUnits, 0) <> 0)