Controlling a chart in Excel with VBA

I am trying to refresh an existing chart where the charted series will change depending on the input by the user:
 - how many funds are to be charted (determined by variable 'reportSize')
 - what series are to be shown (determined by 'wts' where of a possible number of 12 characteristics, only those with weights above zero are included

Here are the problems I am having:
 - I thought it would be easiest to delete the entire Series Collection and then add new series as I need them...the delete method, however, cannot be applied to the whole lot at once
 - When I try to Set wtSeries, I seem to be picking up a single cell, not the range I am trying reference, giving me a error when I try to set the SeriesCollection.Value = wtdSeries (incidentally, 'Set wtNames' works fine as it is a single cell)

The error message is: "Run-Time Error '438': Object does not support this property or method"

Here is the code....any help is much appreciated:

Dim wts() As Double ' gathered from a named range which includes the user weights; series with weights of zero are excluded
Dim m As Integer
Dim n As Integer
Dim wtSeries As Range
Dim wtName As Range
Dim reportSize As Integer ' number of funds to be included in the graph
Dim attribGraph As Object

reportSize = Worksheets("HYRank").Range("reporting")
Set attribGraph = Worksheets("HYReport").ChartObjects("Chart 67").Chart

wtOptions = 12
ReDim wts(wtOptions, 1)

With Worksheets("HYReport").Range("makeChart")
    For n = 1 To wtOptions
        wts(n, 1) = .Cells(1, n)
    Next n
End With

With attribGraph
    n = 1
    For m = 1 To wtOptions
        If wts(m, 1) > 0 Then
            With Worksheets("HYReport")
                Set wtSeries = .Range("attribution")(.Cells(1, m), .Cells(reportSize, m))
                Set wtName = .Range("attribName").Cells(1, m)
            End With
                .SeriesCollection.NewSeries
                .SeriesCollection(n).Name = wtName
                .SeriesCollection(n).Value = wtSeries
        End If
    Next m
End With