Code in 2003 Chart for embedded object to behave as trend line, makes code crash in 2007

Private Sub Worksheet_Activate()
 
Dim shp As Shape
Dim bShape As Boolean
Dim cht As ChartObject
Dim ser As Series
Dim AxisX As Axis, AxisY As Axis
Dim dX As Double, dY As Double, dSlope As Double, dAngle As Double
Dim xData As Variant, yData As Variant
Set cht = ActiveSheet.ChartObjects("chart 10")
Set AxisX = cht.Chart.Axes(xlCategory)
Set AxisY = cht.Chart.Axes(xlValue)
dX = AxisX.Width / (AxisX.MaximumScale - AxisX.MinimumScale)
dY = AxisY.Height / (AxisY.MaximumScale - AxisY.MinimumScale)
For sern = 1 To cht.Chart.SeriesCollection.Count
Set ser = cht.Chart.SeriesCollection(sern)
For Each shp In cht.Chart.Shapes
    Select Case sern
    Case 1
    shname = "redArrow"
    Case 2
    shname = "greenArrow"
    Case 3
    shname = "yellowArrow"
    End Select
    If shp.Name = shname Then
        Exit For
    End If
Next
With ser
    xData = .XValues
    yData = .Values
    dSlope = Application.WorksheetFunction.Slope(yData, xData) * dY / dX
    dAngle = 180 / Application.Pi() * Application.Atan2(1, dSlope)
    If dAngle < 0 Then dAngle = dAngle + 360
    shp.Rotation = -dAngle
End With
Next sern
End Sub