Hey all , I keep getting this error which is hard for me to explain unless show you the code:

Code:
		var xmlHttp;
		  try
		  {
			xmlHttp = new XMLHttpRequest();
		  }catch(e)
		  {
			try
			{
			  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
			}catch(e)
			{
			  try
			  {
				xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
			  }catch(e)
			  {
				alert("Your browser does not support AJAX!")
			  }
			}
		  }
		
		function CustomerRequest(){
			var address = document.getElementById("request").value;
			xmlHttp.onreadystatechange = HandleResponse;
			xmlHttp.open("GET", "ajax.php?address="+address, false);
			xmlHttp.send(null);
		}

		function HandleResponse()
		{
			if (xmlHttp.readyState == 4 && xmlHttp.readyState == 200) {
				RequestXML();
				} else{
				alert("status is " + xmlHttp.status);
				}
		}
		
		function RequestXML()
		{
			xmlHttp.onreadystatechange = ReadXML;
			xmlHttp.open("GET","write.xml",false);
			xmlHttp.send(null);
		}
		
		function ReadXML(){
			if (xmlHttp.readyState == 4 && xmlHttp.readyState == 200)          {
				var xml = xmlHttp.responseXML;
				GenerateMap();
			}else {
				alert ("Status is also "+xmlHttp.status);	
			}
			var addy = xml.documentElement.getElementByTagName('address');
			for (var i=0; i<addy.length; i++)
			{
				var address = add.getAttribute('addy');
				document.write(address);
			}
		}
		function GenerateMap(){
			var map;
			var geocoder;
			geocoder = new google.maps.Geocoder();
			var latlng = new google.maps.LatLng(-34.397, 150.644);
			var myOptions = {
				zoom: 8,
				center: latlng,
				mapTypeId: google.maps.MapTypeId.ROADMAP
			}
			map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
		}
See where I got the line if (ready state == 200), this is where the problem rises. But when I watch fire bug it tells me there was a response of what I expect, what do?

Thank you.