What version and build of Cubase 9 do you have installed (Help, About)? Are you dragging and dropping to an empty area in the Project window? Can you please post a screen shot of what you are seeing?
What version and build of Cubase 9 do you have installed (Help, About)? Are you dragging and dropping to an empty area in the Project window? Can you please post a screen shot of what you are seeing?