Hi David,
Thank you for your interest in Syncfusion Products.
I am afraid I was unable to reproduce the issue. Please refer the sample in this link
http://websamples.syncfusion.com/samples/Chart.Web/6.1.0.34/72390/main.htm where the code you have given renders Line Chart without throwing an exception.
Can you reproduce the issue in this sample so that we can work in depth and send a better solution?
Regards,
Anupama