AJAX validation form error in IE

Hi!

I have this AJAX to make my PHP validation work in real-time.

It's working properly in all web browsers except IE7 and IE8.

IE is popping an error msg:
Row: 71
Error: Unknown runtime error

What am I doing wrong? Tell me if you need more info to help.

The content of getHint.php is nonessential, it's just echoing stuff.

Thanks in advance!

var xmlHttp 
var string
var type
 
function showHint(str) 
{ 
type = str;
 
switch (type)            // Kollar vilken typ
{                        // Är inte kontrollen med, avsluta utan att göra något
case "email":
string = document.getElementById("emailField").value
break;
case "password":
string = document.getElementById("passwordField").value
break;
case "username":
string = document.getElementById("usernameField").value
break;
case "firstname":
string = document.getElementById("firstnameField").value
break;
case "lastname":
string = document.getElementById("lastnameField").value
break;
case "street":
string = document.getElementById("streetField").value
break;
case "zipcode":
string = document.getElementById("zipcodeField").value
break;
case "city":
string = document.getElementById("cityField").value
break;
case "phone":
string = document.getElementById("phoneField").value
break;
 
default:
return;
}
 
if (string.length==0)        // Finns det inget att kolla, töm alla Hint och avsluta
    {
    document.getElementById(type+"Hint").innerHTML = "";
    return;
    }
  
xmlHttp=GetXmlHttpObject(); 
 
if (xmlHttp == null) 
  { 
  alert ("Your browser does not support AJAX!"); 
  return; 
  }  
  
  
var url="gethint.php?"; 
url +="type="+type;
url += "&string="+escape(string);
url +="&sid="+Math.random(); 
xmlHttp.onreadystatechange=stateChanged; 
xmlHttp.open("GET",url,true); 
xmlHttp.send(null);
}  
 
function stateChanged()  
    {  
    if (xmlHttp.readyState==4 || xmlHttp.readyState=="Complete") 
        {  
        document.getElementById(type+"Hint").innerHTML=xmlHttp.responseText; 
        } 
    } 
 
// KONTROLL AV WEBBLÄSARE
 
function GetXmlHttpObject()
    {
    var xmlHttpObject=null;
    try
    {
        //FIREFOX OPERA SAFARI
        xmlHttpObject=new XMLHttpRequest();
    }
    catch (e)
    {
        //IE
        try
        {
            xmlHttpObject=new ActiveXObject("Msxml12.XMLHTTP");
        }
        catch (e)
        {
            xmlHttpObject=new ActiveXObject("Microsoft.XMLHTTP");
        }
    }
    return xmlHttpObject;
}

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