title: Windows Authentication issue in IIS 7.5
body: <p>I'm new to IIS 7.5 and I am trying to get a site working with Windows Authentication. It's an ASP.NET 4.0 application which is set up as an application under the default website and it is running the ASP.NET 4 app pool. The application is set up with Anonymous Authentication disabled and Windows Authentication enabled. </p>
  
  <p>The site is not authenticating properly - I can see an error in the event log (this is a <code>Null Reference</code> error to do with some code that uses <code>Context.User</code>) and the detail says <code>IsAuthenticated=False</code> and the <code>User</code> is blank.</p>
  
  <p>I have set <code>Authentication Mode = Windows</code> under <code>&lt;system.web&gt;</code> in my Web.config and have tried various other config settings without success.</p>
  
  <p>I've tried using the ASP.NET classic app pool but get an error</p>
  
  <blockquote>
    <p>Handler "ExtensionlessUrl-ISAPI-4.0_64bit" has a bad module
    "IsapiModule" in its module list</p>
  </blockquote>
  
  <p>I'd prefer to get it working using the ASP.NET 4 app pool if possible. Can anyone advise what I need to do?</p>