XMLHttpRequest failing on new server

I have the following Javascript function working perfectly on my localhost IIS server. When I migrate the code to my other IIS server (it's a Windows VPS), the xmlhttp.status is always returning as 404 (even though the file that it's checking for is there).

function startInterval(result) {
  //var fname = "http://localhost/excelfiles/Ad_Activity_1_145.csv";
  var path = "http://<% =Request.Url.Host %>/excelfiles/"; 
  var fname = path + a.substring(0,a.length-1) + "_Activity_" + c + '_' + result + '.csv';
  var checkCounter = 0;
  checkInterval = setInterval(function() {
  var xmlhttp = new XMLHttpRequest();
  xmlhttp.open('HEAD', fname);
  xmlhttp.onreadystatechange = handleHttpResponse_check;
  xmlhttp.send(null);

  function handleHttpResponse_check()
  {
    if(xmlhttp.readyState == 4){
      if (xmlhttp.status == 200) {
        //ctrl.innerHTML = '<a onclick="goToURL(\''+fname+'\');return false;">Open file!</a>';
        ctrl.innerHTML = '<a onclick="goToURL(\''+fname+'\');return false;"><img src="images\\Excel_Icon.jpg" style="width:20px;height:20px;cursor:pointer;"/></a>';
        clearInterval(checkInterval);
        } else if (xmlhttp.status == 404) {
          checkCounter += 1;
          if(checkCounter >= 5){
          clearInterval(checkInterval);
          ctrl.innerHTML = 'ERROR: File not created';
          }                                                                                                                 
        }
      }
    }

  }, 1000);
}

I suspect that the XMLHttpRequest is failing on the new server. The fname variable has the right path/filename. The function handleHttpResponse_check function is executing correctly...just that xmlhttp.status is always returning 404 on the new server despite the file being at the path/filename. The localhost server detects the file perfectly and xmlhttp.status returns 200 on that server. Any ideas what might be going on with the new server?

A 404 status code means that the server has not found anything matching the Request-URI. Check the path to the requested resource to ensure that the generated path is the intended path and see if you can access that resource.