Dim lngcombo7 As Long
If IsNull(Me![YourComboName]) Then
Me![YourComboName].Text = ""
Else
lngcombo7 = Me![YourComboName]
Me![YourComboName] = Null
End If
DoCmd.OpenForm "FRM_NameOfFormToAddNewValue", , , , , acDialog
Me![YourComboName].Requery
If lngcombo7 <> 0 Then Me![YourComboName] = lngcombo7