Request redirect to /Account/Login?ReturnUrl=%2f since MVC 3 install on server

We have an internal ASP.NET Webforms application running on a Windows 2008/IIS7 server which has been running fine until we installed MVC3.

Now any requests redirect to /Account/Login?ReturnUrl=%2f.

The website is Webforms not MVC. Because it is an internal only site we have Windows Authentication enabled for the root folder.

We have several other websites on the same server that have not been affected by this problem, but this is the only site where the root folder is set to Windows Authentication.

I solved the problem by adding the following lines to the AppSettings section of my web.config file:

<add key="autoFormsAuthentication" value="false" />
<add key="enableSimpleMembership" value="false"/>

I fixed it this way

1. Go to IIS
2. Select your Project
3. Click on "Authentication"
4. Click on "Anonymous Authentication" > Edit > select "Application pool identity" instead of "Specific User".
5. Done.

Updated answer for MVC 4, heavily borrowed from this page and ASP.NET MVC issue with configuration of forms authentication section (and answered on both pages)

<appSettings>
   ...
   <add key="PreserveLoginUrl" value="true" />
</appSettings>

...

<authentication mode="Forms">
      <forms loginUrl="~/Account/LogOn" timeout="43200" /> <!--43,200 in minutes - 30 days-->
</authentication>

Just remove

 <authorization>
      <deny users="?"/>
    </authorization>

from your web.config file

that did for me