Why is my VS 2011 ASP.NET Project Giving a 401.2 Error When Debugging with IIS Express 7.5?

Question

Everything was working just fine...then one time running the debugger and I'm given a 401.2 error from IIS Express 7.5. I created a new project and tested - worked fine. I ensured the web.config and other project settings where identical - still getting the error in the original project!

(I actually resolved this issue...but haven't seen documentation for this exact issue with my resolution anywhere, I'll add the answer momentarily...Yes, I already reviewed other 401.2 questions on Stackoverflow (and elsewhere) and they are not the same as the issue I was facing...)

Answer 1

In my case, for some reason VS 2011 added a few lines to my applicationhost.config file located under Documents\IISExpress\config. The lines added (and which I removed) where as follows:

    <location path="IRFEmpty">
    <system.webServer>
        <security>
            <authentication>
                <anonymousAuthentication enabled="false" />
                <windowsAuthentication enabled="false" />
            </authentication>
        </security>
    </system.webServer>
    </location>

Don't ask me how they got there - I didn't add them. It is pretty annoying, since all the code in my VS project was 100% correct, it was the IISExpress configuration wrong.

Answer 2

Enable AnonymousAuthentication on the web project... See these instructions for enabling WindowsAuthentication EXCEPT in the same place you can enable AnonymousAuthentication: IIS Express Windows Authentication

In VS2011, debugging my MVC project was working until this setting mysteriously changed to "Disabled" and I began receiving 401.2 error. Enabling this setting fixed the problem.