Hi all, I ran into this same problem when I first started (uh, yesterday!).
The step I was missing was to go to File > Package Project, and choose the platform you’re working with. In my case, it is Android, so I selected "Android (Multi,DXT,ETC2). Then, I was prompted to save, and I chose my project folder root to save in. In my case, I selected **Documents/Unreal Projects/**project-name. This should match the path in your .target error, before the path segment /Binaries.
After this finished processing (took a while), I saved my project and pressed Launch (to my Android device). It was successful, with no .target or UE4Game binary errors.
Looking into my project root folder, I can see the new Binaries folder with the target file.