Proprietà documentelement nulla

[carlomary20]

Salve a tutti, avrei questo problema che riguarda la proprietà documentelement vi posto il codice:

function OGGETTOHTTP() { 
var type_richesta_http; 
var browserutilizzato_http = navigator.appName; 
if(browserutilizzato_http == "Microsoft Internet Explorer"){ 
type_richesta_http = new ActiveXObject("Microsoft.XMLHTTP"); 
}else{ 
type_richesta_http = new XMLHttpRequest(); 
} 
return type_richesta_http; 
}
var HTTPS=OGGETTOHTTP();
// idchat è l'id dell'utente che sta in conversazione con noi
var IDCHAT=1;
return mes_chat();
function mes_chat(){

	  HTTPS.open("GET", "messaging_instant_chat2.php?id="+IDCHAT);
	  HTTPS.onreadystatechange = stampamexchat; 
          HTTPS.send(null);
}
function stampamexchat()
{	
  if (HTTPS.readyState == 4)
  {
  
	
	var response=HTTPS.responseText;
	response=HTTPS.responseXML.documentElement;
	idArray=response.getElementsByTagName("id");
	nameArray=response.getElementsByTagName("name");
	timeArray=response.getElementsByTagName("time");
	messageArray=response.getElementsByTagName("message");
	stampamessaggipresi(idArray, nameArray, timeArray, messageArray, IDCHAT);	
   
	
  }
}
function stampamessaggipresi(idArray, nameArray, timeArray, messageArray, IDCHAT){
	for (var i=0; i<idArray.length; i++)
	{
		var time=timeArray.item(i).firstChild.data.toString();
		var name=nameArray.item(i).firstChild.data.toString();
		var message=messageArray.item(i).firstChild.data.toString();
		var htmlmessage="<div id=\"messaggiochat\"><div id=\"titlechats\">Ore: "+time+" "+name+" :</div><div id=\"messaggiotestochat\">"+message+"</div>";
		displaymessage(htmlmessage, IDCHAT);
	}	
	
}

function displaymessage(messagee, IDCHAT){
var TCZ = document.getElementById("instant_messages"+IDCHAT);
	 TCZ.innerHTML +=messagee;
	  var scrolling=document.getElementById('contenitore_messaggi'+IDCHAT); 
   
    scrolling.scrollTop=scrolling.scrollHeight;
}
}

<?php
header('Content-type: text/html;charset=iso-8859-9');
session_start();
include('ffdsffsd/dsfdsg.inc');    
    
$db=mysql_connect($ip_host, $user_host, $pass_host) or die("parametri errati");
$name=mysql_select_db($name_host)  or die("database inesistente");
$data_set=date('Y-m-d H:i:s');

$messages=@mysql_query("SELECT * FROM chat_conversazioni  where (id_user='" . $_SESSION[ID] . "' or id_user='" . $_GET['id'] . "') AND (id_user_friend='" . $_SESSION[ID] . "' or id_user_friend='" . $_GET['id'] . "') ORDER BY data_chatting ASC limit 10");
$response = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';
$response .='<response>';
if(@mysql_num_rows($messages)>0){
    while($rows=@mysql_fetch_array($messages)){
        $id=$rows['ID'];
        $idnomecognome=$rows['id_user_friend'];
        $time=$rows['ora_instant_mess'];
        $message=$rows['messaggio_chat'];
        $nomecognomes=@mysql_query("SELECT * FROM user where id_user='" . $nomecognome . "'");
        $cognomenome=@mysql_fetch_array($nomecognomes);
        $nomcog=$cognomenome['nome'] . " " . $cognomenome['cognome'];
        $response .='<id>' . $id . '</id>' . '<time>' . $time . '</time>' . '<name>' . $nomcog . '</name>' . '<message>' . $message . '</message>';
    }
    $messages->close();
}
$response=$response . '</response>';
return $response;