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 a problem of same type. Running my site published on IIS, the same error was shown.

I saw a web.config file in the wwwroot folder (out of application folder). I removed this file and the application ran OK.

Look for a web.config file placed in a wrong folder (above your folder application).

Good luck!