Here is the answer provided in your support ticket:
ChartSeries' PlotArea property is only populated when the series is added to RadChart Series collection. The line of code you have pointed tries to access the PlotArea
property of the series before it has been added to the chart's
collection. Still, currently RadChart can have only one PlotArea, so it
is safe to access it like this: RadChart1.PlotArea...
Hope this helps.
the Telerik team
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