Invalid parameter error when method is called from another sub - excel

Question

I have the below code that creates charts from some worksheets and put the charts in their own worksheets. When I run the macro on it's own it works perfectly. When I use Call InsertDNCCharts from another macro I get a "Invalid Parameter" error on .Period = 7 from within the With tl block. Why is there a difference? If the code runs on its own shouldn't it run the same way when called from another sub?
Sub InsertDNCCharts()
Dim ws As Worksheet
Dim cws As Worksheet
Dim country As String
Dim lastrow As Long
Dim chrt As Shape
Dim chrtname As String
Dim xvalues As Range
Dim yvalues As Range
Dim tl As Trendline
For Each ws In ThisWorkbook.Worksheets
If Right(ws.Name, 6) = "_Chart" Then
country = Left(ws.Name, Len(ws.Name) - 6)
Set cws = ThisWorkbook.Worksheets(country)
lastrow = cws.Cells(Rows.count, "c").End(xlUp).Row
Set xvalues = cws.Range("c5:c" & lastrow)
Set yvalues = cws.Range("l5:l" & lastrow)
cws.Activate
Application.Union(xvalues, yvalues).Select
Set chrt = cws.Shapes.AddChart2(201, xlColumnClustered, Cells(5, 2).Left, Cells(5, 2).Top, 1000, 420)
chrt.Name = ws.Name
chrtname = chrt.Name
cws.Cells(5, 1).Select
With chrt.Chart
.Location Where:=xlLocationAsObject, Name:=ws.Name
.Axes(xlCategory).HasMajorGridlines = True
.Axes(xlCategory).HasMinorGridlines = False
.Axes(xlValue).HasMajorGridlines = True
.Axes(xlValue).HasMinorGridlines = False
.HasLegend = False
End With
ws.ChartObjects(chrtname).Activate
ActiveChart.ChartWizard Title:=country & " Daily New Cases (DNC)"
Set tl = ws.ChartObjects(chrtname).Chart.SeriesCollection(1).Trendlines.Add
With tl
.Type = xlMovingAvg
.Period = 7 '*******Error on this line. Debug says period=2, which is the default moving average period.
.DisplayEquation = False
.DisplayRSquared = False
.Format.Line.DashStyle = msoLineSysDot
.Format.Line.Weight = 3.5
.Format.Line.ForeColor.RGB = RGB(255, 0, 0)
.Format.Line.Style = msoLineSingle
End With
End If
Next ws
End Sub

Answer 1

If the chart in discussion (the created one) has at least 7 points, it is possible that the code is not referring to the appropriate chart, or the chart has not been created as necessary.
In order to check that, I would suggest you putting a break point on line With tl and visually check if the active chart is the one you need and if it looks as expected. It looks that the problem has to be before the line raising the error.