Cannot get past Run-time 70, Permission Denied

[Mordred]

Hi all,
I just opened a file I was working on last night and when I stepped through the code, which is

Private Sub ComboBox2_Change()
Dim Rng1 As Range, Col As Long, cbAddItm As Long
    Col = Sheets("Qtly").Cells(5, Columns.Count).End(xlToLeft).Column
Debug.Print Sheets("Qtly").Cells(5, 3).Address
With ComboBox2
    For cbAddItm = 3 To Col
        .AddItem Sheets("Qtly").Cells(5, cbAddItm)
    Next cbAddItm
End With
End Sub

I am now prompted with an error at the AddItem line telling me that my permission is denied, run-time 70. What's this about, any ideas?

Regards: