Thank you for your sample project and detailed explanation! I can
understand your question now.
When I run the sample application, I see the ROReport and ROChild reports
are displayed properly. However, the ROGrandChild report isn't shown,
instead, I see an error text "Error: Subreport could not be shown".
I make the following modifications on your sample project and all the three
reports could be displayed correctly on my side:
1. Open the ROGrandChild.rdlc in the designer and set the 'Copy to Output
Directory' property to 'Copy if newer' in the Properties window.
2. Open the ROChild.rdlc in the designer. Right click the subreport on the
ROChild report and choose Properties. In the Subreport Properties window,
switch to Parameters tab and add a parameter in the list. The parameter
name is 'ROID' and the parameter value is '=Fields!Key.Value'.
Please try this on your side to see if it solves the problem and let me
know the result.
If you have anything unclear, please feel free to let me know.
Microsoft Online Community Support