IIS express: Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to

Question

In Visual studio, Solution->Web.Project->Properties->Web, I have changed my Project Url from http://localhost:51123/ to http://localhost:51123/NewProj

Answer 1

I had the same problem. It turned out that I had a different project that uses IISExpress with the same port number. Once I changed the project to use a different port number, the error went away.