Do you have Attach bookmark created? When you are working with object you are creating bookmarks resposible for different things in your obcject(login, start etc) you need to create Attach bookmark.
I never had any problems with attaching to app, except mainframe app.
Copy your Navigate step from Launch bookmark, then create new one(call it attach) and paste that Navigate step. Then Edit it, Chane from launch to attach and in Properties you need to fill "Window Title" and "Process Title". Window title, you have it at the top window bar. Process title, youll find it in Windows Task Menager - Processes.
Hope it helps!