Cannot call StartAt when content generation is in progress

[Oliver]

I'm getting this error when rendering a Horizontal Bar or Horizontal Stacked Bar

Error appeared when running:
radChart1.SeriesMappings.Add(seriesMapping);

I have no problems when I'm rendering other types of charts.
Anyone knows about this error?

[Oliver]

I've changed the program slightly to set the ItemsSource at individual seriesMapping level instead to RadChart.ItemsSource. That seem to solve it.