Xml load issues

Ok I used the wonderful xml tute you have here and it’s great but i slightly altered it for my needs and have this method

private function loadXML(p_page:String){
    __page = p_page;
    __us_txt = new XML;
    __us_txt.ignoreWhite = true;
    __us_txt.onLoad = function(success){
    if (success){


in the above code traceing this outputs the xml file as expected, but I can’t access this.firstChild… etc
I assume I am doing something wrong can anyone point out what that was and help.