I am building a fairly simple report with a subreport in Visual Studio 2015, using RDLC files. The main report shows a list of Workshops assigned to a Conference and renders fine without the subreport. The subreport shows a list of Attendees for each Workshop, and also renders fine on its own (I merely specify the Workshop ID as the parameter and I get the appropriate list of Attendees).
I am populating the data sources with data by adding new ReportDataSource objects in the code-behind of the page housing the report viewer. As soon as I set the subreport's data in the SubreportProcessing event, though, I get an error stating that reporting services cannot create a data reader for a data source in the parent report.
I debugged, set a breakpoint, and verified that the main report's data source is properly set while the code in my SubreportProcessing event is executing, before and after setting the subreport's data source.
Is it possible that setting the subreport's data source is somehow invalidating the parent report's data source?