Keeps redirected to 401 Unauthorized page

Hello,

I keep redirected to a "401 Unauthorized" page, which is the Login page. It first loads a 302 Found (Failed to load source for: http://localhost:4558) page then
the redirection.

        <!--<authentication mode="Forms">
            <forms loginUrl="~/Login" timeout="2880"/>
        </authentication>-->


Everything works well when I comment the attribute Authentication at web.config or if after I logged-in.

Before this happens, I delete all files at (C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files). Don't you think this is the reason?

I'm under MVC, even if I remove the action filter Authorize(), I still get redirected to 401.

        </httpModules>
  ...