Second Version: This has helped me too.
Copy project to external disk.
Deleting Intermidiate, Saved, binaries .vs and .sln project I then clicked on Generate visual studio project files. After that I also clicked on the Unreal Engine executable to run it and it requested to rebuild it which I allowed and the editor started.
After that I opened the visual studio solution.
When trying to then ctrl+F5 the project I had the encountered the Unable to start debugging error.
So setting my project (the one that is under Games in the Solution Explorer) to Set as Startup Project" solved it!