new URLLoader() broken in AIR 21 + [HELP]

Any idea why line 6 is crashing in AIR 21 but works fine in AIR 20 and below ?

    sendHeader = new URLRequestHeader("Content-type","application/octet-stream");
    sendReq = new URLRequest(phpPath);
    sendReq.requestHeaders.push(sendHeader);
    sendReq.method = URLRequestMethod.POST;
   
    sendLoader = new URLLoader();
    sendLoader.addEventListener(Event.COMPLETE,imageSentHandler);
  sendLoader.addEventListener(ErrorEvent.ERROR, onError);