Series Problem

[aMember]

Having problems with modifying a series through VBA.

Can anyone see why
"Unable to set the Values Property of the Series Class"
would occur on the line:
ActiveChart.SeriesCollection(i).Values = DataWindow


Using Excel 97 on NT4.0
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ActiveSheet.ChartObjects("Chart 1&quot.Activate
Dim DateWindow As Range
FirstInWindow = Sheets("Data&quot.Cells(DateRow, OldestMonthCol).Address
LastInWindow = Sheets("Data&quot.Cells(DateRow, NewestMonthCol).Address
Set DateWindow = Sheets("Data&quot.Range(FirstInWindow, LastInWindow)

Dim DataWindow As Range

For i = 1 To ActiveChart.SeriesCollection.Count
Select Case i
Case 1
theRow = Sheets("Data&quot.Range("CPIData&quot.Row
Case 2
theRow = Sheets("Data&quot.Range("SPIData&quot.Row
Case 3
theRow = Sheets("Data&quot.Range("BACEAC4Data&quot.Row
End Select
'set the range for the window of dates in view
FirstInWindow= Sheets("Data&quot.Cells(theRow, OldestMonthCol).Address
LastInWindow= Sheets("Data&quot.Cells(theRow, NewestMonthCol).Address
Set DataWindow = Sheets("Data&quot.Range(FirstInWindow, LastInWindow)

ActiveSheet.ChartObjects(1).Activate
ActiveChart.SeriesCollection(i).Values = DataWindow
ActiveChart.SeriesCollection(i).XValues = DateWindow

Next i