Hi John,
It may be related to the settings of IIS on the sever (some settings won't allow you to generate axd files, cause the server will require the file to exist). You can use image response to check if this is the case - in the code behind write:
nChartControl1.ImageAcquisitionMode = Nevron.UI.WebForm.Controls.ClientSideImageAcquisitionMode.TempFile;
this will instruct the control to generate a temporary file in the NevronTemp directory which must be present under the website root directory. The ASP.NET account must have read, write and modify permissions for this folder.
Hope this helps - let me know if the problem persist.
Best regards,
Bob