Probleme de combobox dans formulaire

Option Explicit

Dim Ws As Worksheet
Dim NbLignes As Integer

Private Sub UserForm3_Initialize()
     Set Ws = Worksheets("Base")
     NbLignes = Ws.Range("A65536").End(xlUp).Row
  
    Alim_Combo 1
End Sub

Private Sub ComboBox1_Change()
      Alim_Combo 2, ComboBox1.Value
End Sub


Private Sub ComboBox2_Change()
    Alim_Combo 3, ComboBox2.Value
End Sub

Private Sub ComboBox3_Change()
    Alim_Combo 4, ComboBox3.Value
End Sub

Private Sub Alim_Combo(CbxIndex As Integer, Optional Cible As Variant)
    Dim j As Integer
    Dim Obj As Control
    Set Obj = Me.Controls("ComboBox" & CbxIndex)
    Obj.Clear
    If CbxIndex = 1 Then
        For j = 2 To NbLignes
            Obj = Ws.Range("A" & j)
            'Remplit le ComboBox sans doublons
            If Obj.ListIndex = -1 Then Obj.AddItem Ws.Range("A" & j)
        Next j
    Else
        For j = 2 To NbLignes
            If Ws.Range("A" & j).Offset(0, CbxIndex - 2) = Cible Then
                Obj = Ws.Range("A" & j).Offset(0, CbxIndex - 1)
                If Obj.ListIndex = -1 Then Obj.AddItem Ws.Range("A" & j).Offset(0, CbxIndex - 1)
            End If
        Next j
   End If
End Sub

Configuration: Windows XP
Firefox 2.1
EXCEL 2007