Ajax works in FF but fails 50 % in IE 7. please help

[2levelsabove]

The req.open doesnt even get called sometimes in IE and thus nothing gets returned.

Works perfectly in FF

function GetCarModels(makeID)
{

var d = document;
var f = d.forms['rideinfo'];	

	if (window.XMLHttpRequest) {
		var	req = new XMLHttpRequest();
	}
	else if (window.ActiveXObject) {
		var req = new ActiveXObject("Microsoft.XMLHTTP");
	}
	req.open("GET", "include/_process/getmodels.php?json=1&makeID="+makeID, true);
	req.setRequestHeader('Content-Type', 'application/json');
	req.send(null);
	req.onreadystatechange = function() {
		if ((req.readyState == 4) && (req.status == 200)) {


			var jsonContacts = eval('(' + req.responseText + ')');




				f.model.options.length = 0;
				f.model.options[0] = new Option("All",0);

				for (var x = 0; x < jsonContacts.length; x++) {

				d.getElementById("model").options[x+1] = new Option(jsonContacts[x].model,jsonContacts[x].atrModelsID);

				//HELLO!!!!
			}//for loop

		}
	}

}//function

[Kudose]

I use this code for my ajax requests and haven't had an issue.

var request = null;

function createRequest(){
  try {
    request = new XMLHttpRequest();
  } catch (trymicrosoft){
    try {
      request = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (othermicrosoft) {
      try {
        request = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (failed) {
        request = null;
      }
    }
  }

  if(request == null){
    alert("Error creating request object.");
  }

}

Your 50% probably uses ActiveXObject("Msxml2.XMLHTTP")