Compile Error:Method or Data Member Not Found

Hi All,
I have three combo boxes in Sheet7. The moment I open the Workbook, the following error pops up;
"Compile Error:
Method or Data Member Not Found"

I have used the following codes to run the combo boxes.

PHP Code: 

Private Sub ComboBox1_Change()
    Me.ComboBox2.Clear
    Me.ComboBox3.Clear
    If Me.ComboBox1.Text = vbNullString Then Exit Sub
    Dim ListCell As Range
    For Each ListCell In Sheet1.Range(Me.ComboBox1.List(Me.ComboBox1.ListIndex))
    Me.ComboBox2.AddItem (ListCell.Value)
    Next ListCell
    End Sub
Private Sub ComboBox2_Change()
    Me.ComboBox3.Clear
    Dim ListCell As Range
    If Me.ComboBox2.Text = vbNullString Then Exit Sub
    For Each ListCell In Sheet1.Range(Me.ComboBox2.List(Me.ComboBox2.ListIndex))
    Me.ComboBox3.AddItem (ListCell.Value)
    Next ListCell
    End Sub 


How do I get rid of this error message.
Thanks
Lok