The source of my SubReport was in a nested class and in the preview of the main report I received the error "Invalid report type" although the same nested class was successfully discovered in the VS designer with the assembly-qualified name 'Test.Class1+DetailReport1, Test, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

When I tried using a class (without a nested class, e.g., 'Test.DetailReport1, Test, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null') then I could get the subreport to render within the main report.

It could be the syntax for the qualified name is not handling nested classes.