Probleme mit DropDown-Menü seit IE 9

Hallo,

Ich habe auf einer Seite folgenden Quellcode:

function webClient() {

  var i;

  this.IE    = false;
  this.NS    = false;
  this.OP    = false; 
  this.release = null;
  
  if ((i = navigator.userAgent.indexOf("Opera")) >= 0) {
    this.OP = true;
    this.version = parseFloat(navigator.userAgent.substr(i + 5));
    return;
  }

  
  if ((i = navigator.userAgent.indexOf("MSIE")) >= 0) {
    this.IE = true;
    this.release = parseFloat(navigator.userAgent.substr(i + 4));
    return;
  }

  if ((i = navigator.userAgent.indexOf("Netscape6/")) >= 0) {
    this.NS = true;
    this.release = parseFloat(navigator.userAgent.substr(i + 10));
    return;
  }

  if ((i = navigator.userAgent.indexOf("Netscape7/")) >= 0) {
    this.NS = true;
    this.release = parseFloat(navigator.userAgent.substr(i + 10));
    return;
  }

  if ((i = navigator.userAgent.indexOf("Gecko")) >= 0) {
    this.NS = true;
    this.release = 6.1;
    return;
  }
}


var webClient = new webClient();

var activeButton = null;
var activeSubButton = null;

 if (webClient.IE)
	 document.onmousedown = pageMouseDown;
  else
     document.addEventListener("mousedown", pageMouseDown, true);

function pageMouseDown(event) {

  var el;
  
  //if (activeButton == null)
  //  return;

  if (webClient.IE)
    el = window.event.srcElement;
  else
    el = (event.target.tagName ? event.target : event.target.parentNode);

  if (el == activeButton || el == activeSubButton)
    return;

  if (el.className != "menuButton"  && el.className != "menuItem" &&
      el.className != "menuItemSep" && el.className != "menu") {
	    if (activeButton) closeMenu(activeButton);
    	if (activeSubButton) closeSubMenu(activeSubButton);
	}
}

function menuTouch(event, menuName) {
  var button;
  if (webClient.IE)
    button = window.event.srcElement;
  else
    button = (event.target.tagName ? event.target : event.target.parentNode);

  if (!button.menu && menuName)
    button.menu = document.getElementById(menuName);

  if (activeButton && activeButton != button)
    closeMenu(activeButton);
  if (activeSubButton && activeSubButton != button)
    closeSubMenu(activeSubButton);
	
  if (!button.isactive)
  	if (menuName) {
	    openMenu(button);
	//} else {
	//	activeButton=button;
	//	button.isactive=true;
	//	button.className = "menuButtonActive";
	}
  return false;
}

function subMenuTouch(event, menuName) {
  var button;

  if (webClient.IE)
    button = window.event.srcElement;
  else
    button = (event.target.tagName ? event.target : event.target.parentNode);

  if (!button.menu && menuName)
    button.menu = document.getElementById(menuName);

  if (activeSubButton && activeSubButton != button)
    closeSubMenu(activeSubButton);

  if (!button.isactive && menuName)
    openSubMenu(button);

  return false;
}

function openSubMenu(button) {

  var w, dw, x, y;

  button.className = "menuItemActive";  
  
  if (webClient.IE && !button.menu.firstChild.style.width) {
    w = button.menu.firstChild.offsetWidth;
    button.menu.firstChild.style.width = w + "px";
    dw = button.menu.firstChild.offsetWidth - w;
    w -= dw;
    button.menu.firstChild.style.width = w + "px";
  }

  x = getPageOffsetLeft(button)+ button.offsetWidth;;
  y = getPageOffsetTop(button);

  x++;
  y++;
  
  button.menu.style.left = x + "px";
  button.menu.style.top  = y + "px";
  button.menu.style.visibility = "visible";

  button.isactive = true;
  activeSubButton = button;
}

function openMenu(button) {

  var w, dw, x, y;

  button.className = "menuButtonActive";

  if (webClient.IE && !button.menu.firstChild.style.width) {
    w = button.menu.firstChild.offsetWidth;
    button.menu.firstChild.style.width = w + "px";
    dw = button.menu.firstChild.offsetWidth - w;
    w -= dw;
    button.menu.firstChild.style.width = w + "px";
  }

  x = getPageOffsetLeft(button)-1;  

  y = getPageOffsetTop(button) + button.offsetHeight;

  button.menu.style.left = x + "px";
  button.menu.style.top  = y + "px";
  button.menu.style.visibility = "visible";

  button.isactive = true;
  activeButton = button;
}

function closeMenu(button) {
  button.className = "menuButton";

  if (button.menu) button.menu.style.visibility = "hidden";

  button.isactive = false;
  activeButton = null;
}

function closeSubMenu(button) {
  button.className = "menuItem";

  if (button.menu) button.menu.style.visibility = "hidden";

  button.isactive = false;
  activeSubButton = null;
}


function getPageOffsetLeft(el) {
  return el.offsetLeft + (el.offsetParent ? getPageOffsetLeft(el.offsetParent) : 0);
}

function getPageOffsetTop(el) {
  return el.offsetTop + (el.offsetParent ? getPageOffsetTop(el.offsetParent) : 0);
}

Leider funktioniert jetzt seit Internet Explorer 9 das DropDown-Menü nicht mehr.

Hat jemand eine Idee an was das liegen k?nnte und was ich ?ndern muss?

VIELEN DANK schon mal!!

Gru?

Matthias