Cascading ComboBox Runtime Error

Im getting a runtime error 380, invalid property value.

Any Ideas?

Private Sub ComMotSCM_Change()

Dim strRange As String
    If ComMotSCM.ListIndex > -1 Then
       strRange = ComMOTcm
       Labeltest.Caption = strRange
       strRange = Replace(strRange, " ", "_")
            With ComMOTcm
                .RowSource = vbNullString
                .RowSource = strRange
                .ListIndex = 0
            End With
    Else
       Labeltest.Caption = "CM"
    End If
End Sub