Unable to get named range in Excel

I have a worksheet where there is a chart on the first sheet, showing some data from a named range.
The named range looks like this:

=OFFSET(chart_data!$B$2,0,0,COUNTA(chart_data!$B:$B)-1)

where chart_data is a different sheet.
I also have a VBA script that is supposed to set colors of the chart same as background colors of corresponding cells. The script follows:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim cht As ChartObject
Dim i As Integer
Dim vntValues As Variant
Dim s As String
Dim myseries As Series
Dim nRange As Range

    For Each cht In ActiveSheet.ChartObjects
        For Each myseries In cht.Chart.SeriesCollection

            If myseries.ChartType <> xlPie Then GoTo SkipNotPie
            s = Split(myseries.Formula, ",")(2)
            vntValues = myseries.Values                

            For i = 1 To UBound(vntValues)
                If Range(s).Cells(i).Interior.Color <> 16777215 Then
                    myseries.Points(i).Interior.Color = Range(s).Cells(i).Interior.Color
                End If
            Next i
SkipNotPie:
        Next myseries
    Next cht
End Sub

My problem is that when I try to evaluate Range(s), where s = "report!values_list", I get

Run-time error '1004':
Method 'Range' of object '_Worksheet' failed

How can I solve this?