Unable to start debugging. The startup project could not be launched. VS2015

Question

I have started a new console project in VS2015. I only have this code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text         


        

Answer 1

Additionally to "Unable to start debugging" I also had errors "The operation could not be completed: Unspecified error" when I tried to rebuild.
Thanks to Visual Studio popup: "the operation could not be completed" it was enough to close Visual Studio 2015 and then open again.