adds-in of power point 2013 crash when new XMLHttpRequest invoke open in javascript

the adds-in can work well before version  ppt2010, but when i deploy it in the ppt2013, in js codes, xmlHttp.open("GET", url, true)  will crash catch exception "object error" "undefined".

Please help me, i am sticked for two days.

 if (window.XMLHttpRequest) {
   xmlHttp = new XMLHttpRequest();
   if (xmlHttp != null)           
      alert("xmlhttprequest ok!");
}
else if (window.ActiveXObject) 
{
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
if (xmlHttp != null)           
      alert("Microsoft xmlhttp ok!");
}

    .....................................

xmlHttp.open("GET", url, true); /////////crash here. object undefined