Hi Rajasekaran,
Thanks for your interest in Syncfusion products.
I think your aren't add the Diagram Handlers.The DiagramWebControl uses a custom HTTP handler for processing client requests for rendering the diagram image onto the Web page. While creating diagrams using the DiagramWebControl, defining httphandlers with the "*" verb, path and type attributes is mandatory.
The "*" verb is used to place no restrictions on the types of requests serviced by the handler. The path attribute specifies the point name to be mapped to the handler, and the type attribute specifies the type and syncfusion assemblies from which the type should be loaded to service requests.
Please let me know if this helps !.
Thanks,
Ramesh M