[ajax] this._XmlHttp has no properties

[mascalzone]

Errore: this._XmlHttp has no properties
File sorgente: ajax.js
Riga: 91

qual'è l'errore?

vi posto il codice interessato....

function ARRT (mode)
{	this._XmlHttp=false;	
	this._Mode=(mode=='xml')?'responseXML':'responseText';
	this.Error=this._SetObj();		
	this.Result=false;
}

ARRT.prototype._SetObj	=	function()
{	if(window.XMLHttpRequest) 
	{	this._XmlHttp = new XMLHttpRequest(); 
		return false;
	}else	if(window.ActiveXObject)
		{ try{	this._XmlHttp = new ActiveXObject("MSXML2.XMLHTTP");
			return false;
		     }
		  catch(e)
			{ this._XmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); 
			 return false;
			}
		}
	return true;
}


ARRT.prototype.Request	=	function (url, dati, async)
{
if (!this.Error)
{ if (dati=='')
  {// Metodo GET
    this._XmlHttp.open('GET', url, async);
    }else
  {// Metodo POST
    this._XmlHttp.open("POST", url, async);
    this._XmlHttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    this._XmlHttp.setRequestHeader("Content-length",dati.length);
    this._XmlHttp.setRequestHeader("Connection","close");
  }	

  this._XmlHttp.onreadystatechange	=	function()
  {if ( this._XmlHttp.readyState == 4 )
	{if ( this._XmlHttp.status == 200 )
	  {this.Result = this._XmlHttp+'.'+this._Mode;
	  }
	  else
	  {this.Error = this._XmlHttp.status;
	  }
	}
  }
  this._XmlHttp.send(null)
}
}

il codice sopra è in un file esterno che includo
e per chiamarla....

<script language="Javascript">
function ajax(s)
{	r= new ARRT('text');
	if (!r.Errore)	r.Request('t.php?ciao=fra','',true);
}
</script>