Hi Aubrey Ivan,
The Html5 Viewer uses Telerik Reporting REST Service to deliver reports - check HTML5 Report Viewer and Reporting REST services. The client-side reportSource is a property of the viewer that contains a report identifier and collection with parameter values. It cannot contain a report instance. The message is received because InstaceReportSource is not supported by the Html5 Viewer (including its MVC wrapper).
If you need to instantiate a report, for example, in order to set its DataSource, you need to do this in a Custom Report Resolver in the REST Service. The Resolve() method of the resolver will receive as an argument the reportSource.report property. With the MvcViewer in the case of TypeReportSource, this will be the assembly qualified name of the report class, i.e. the TypeName. You need to instantiate the report based on this information and set its data source as required. Then you may return the modified report wrapped in an InstanceReportSource from the Resolve method - it will be passed to the Reporting engine. Hence, the logic for assigning a data source to the Report should be moved to the Resolve method of a custom report resolver.
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