[AccessD] Combo Box Question

I have a form with two text boxes and a combo box. I use the following code to  display a value in the combo box when the form opens. The code then shifts the focus to the first text box. I have code attached to the combo. It runs fine if I select something from the drop down list but does not run if I click on the default value that is displayed in the combo box. If I select another item in the drop down list and then go back and select the default value displayed the code then runs. I think the problem has to do with selecting something from the combo box list but I am unsure how to proceed. Thanks.

Form opening code

Private Sub Form_Open(Cancel As Integer)
    Me.WellNumber.SetFocus
    Me.WellNumber.ListIndex = 0
    Me.StartDate.SetFocus
End Sub

Combo box code

Private Sub WellNumber_Click()
    Dim frm As Form, ctl As Control
    Dim varItm As Variant, X As Variant
    Set frm = [Forms]![frm Set Down Report Options]
    Set ctl = frm!WellNumber
    DoCmd.SetWarnings Off
    'get the row number of the selected row in the list box
    varItm = ctl.ListIndex

    Select Case varItm
        Case 0 'all wells
             DoCmd.OpenReport "rpt Set Down All", acViewReport
        Case Else
             DoCmd.OpenReport "rpt Set Down in a Time Interval", acViewReport
    End Select
    'Stop
End Sub