Thank you for contacting us. I see in your picture you use our RadChart
control, however, you can try our new RadChartView
control which provides new features and performance optimizations. You can read more about the difference between the two controls in this article
Let me now get to your issue. We strongly recommend you to upgrade to out latest release and try to reproduce this exception with it. If you reproduce the issue, it will be great to sent a sample runnable project to us so we can further investigate.
All the best,
Pavel R. Pavlov
the Telerik team