title: ASP.NET FileContentResult always 404 in production
body: <p>I have an ASP.NET MVC 3 web app that's behaving strangely. There's an action that allows me to download a test file:</p>
  
  <pre><code>    [HttpGet]
      public ActionResult Download()
      {
          var cd = new System.Net.Mime.ContentDisposition
              {
                  FileName = "test_file.txt",
                  Inline = false,
              };
  
          Response.AppendHeader("Content-Disposition", cd.ToString());
          return File(System.Text.Encoding.Unicode.GetBytes("HELLO THERE"), "text/plain");
      }
  </code></pre>
  
  <p>In debug mode it works no problem, I get a file download as expected ("test_file.txt", with contents "HELLO THERE").</p>
  
  <p>When published, and deployed with IIS 6, a 404 error is always returned. Anyone know why the difference and how to fix it?</p>