I am getting this Error

NETWORK_ERROR: XMLHttpRequest Exception 101

when trying to get XML content from one site. Here is my code

var xmlhttp; 
if(window.XMLHttpRequest)
        { 
            xmlhttp = new XMLHttpRequest();
        }
         if (xmlhttp==null)
        {
            alert ("Your browser does not support XMLHTTP!");
            return;
        }         

xmlhttp.onReadyStateChange=function() 
        {
                if(xmlhttp.readyState==4)
                {
                var value =xmlhttp.responseXML;
                alert(value);
                }
         } 
        xmlhttp.open("GET",url,false);
        xmlhttp.send();
        //alert(xmlhttp.responseXML);      
     }
xmlhttp.open("GET",url,false);
xmlhttp.send(null);

Does any one have a solution?