'null' is null or not an object error on javascript

I have this code in my HEAD :
 
<script type="text/javascript" src="mootools.v1.11.js"></script>
<script type="text/javascript" src="mooticker.js"></script>
  <script type="text/javascript">
    // Create ticker at domready state
    window.addEvent('domready',function() {
      var myTicker = new Ticker('newsticker',{toggleButton:'toggle'});
    });
  </script>
 
 
 
 
and this code in my BODY:
 
<div id="newsSubContainer">
  <div id="newsticker">
    <ul>
      <li>TEST 1</li>
      <li>TEST 2</li>
      <li>TEST 3</li>
      <li>TEST 4</li>
    </ul>
  </div>
  <div id="toggle"></div>
</div>
 
 
 
 
Here is the code from mooticker.js if it may help:
 
// mooticker - Newsticker class
// Original copyright 2006 Wolfgang Bartelme, Bartelme Design - http://bartelme.at
//
// Ported and edited for mootools by Huug Helmink, Ace Group bv - http://www.acegroup.nl
// version 0.2
// date 2007-09-26
//
//
// moootools v.11 classes
// Core: Core
// Class: Class, Class.Extras
// Native: Array, String, Function, Number, Element
// Element: Element.Event, Element.Filters, Element.Selectors
// Window: Window.DomReady
// Effects: Fx.Base, Fx.CSS, Fx.Style
//
//
// Usage:
// var myTicker = new Ticker('idOfDivElement');
//     or (with options)
// var myTicker = new Ticker('idOfDivElement',{toggleButton:'idOfToggleDiv',interval:####});
// with #### as an integer > 2000
//
//
var Ticker = new Class({
  // Define options
  options: {
    toggleButton: false,
    interval: 5000
  },
  
  initialize: function(containerId,options) {
    // Declare variables
    var Appear,myFade,myBlinder;
  
    // Set container div
    this.container = $(containerId);
    // Set options
    this.setOptions(options);
    this.interval = this.options.interval;
    this.toggleButton = $(this.options.toggleButton);
 
    this.messages = $(this.container).getElements('li');
    this.number_of_messages = this.messages.length;
    if (this.number_of_messages == 0) {
      this.showError();
      return false;
    }
    this.current_message = 0;
    this.previous_message = null;
 
    // Create toggle button when ID is supplied with options
    if (this.toggleButton != false) {
      this.toggle_button = new Element('a').setProperties({
        'href': 'http://www.infinitymotorcycles.com/news.asp',
        'id': 'togglenewsticker'
      }).setHTML('More...').addEvent('click',this.toggleTicker.bind(this));
   
      this.toggleButton.adopt(this.toggle_button);
    }
    
    // Display first message
    this.hideMessages();
    this.showMessage();
    // Install timer
    this.timer = this.showMessage.periodical(this.interval,this);
  },
 
  showMessage: function() {
    Appear = new Fx.Style(this.messages[this.current_message],'opacity',{onStart:function(item) {
      item.setStyle('display','block');
    }}).start(0,1);
    this.fadeMessage.delay(this.interval-2000,this);
    if (this.current_message < this.number_of_messages-1) {
      this.previous_message = this.current_message++;
    } else {
      this.current_message  = 0;
      this.previous_message = this.number_of_messages - 1;
    }
  },
 
  fadeMessage: function() {
    myFade = new Fx.Style(this.messages[this.previous_message],'opacity',{onComplete:function(item) {
      item.setStyle('display','none');
    }}).start(1,0);
  },
 
  hideMessages: function() { 
    this.messages.each(function(message) { 
      message.setStyles({
        'display': 'none',
        'opacity': 0
      });
    })
  },
 
  toggleTicker: function() {
    myBlinder = new Fx.Slide(this.container,{duration:1000});
  },
 
  // Display error message when there is no list, or the list is empty
  showError: function() {
    if ($ES('ul',this.container).length == 0) {
      this.list = new Element('ul');
      this.container.adopt(this.list);
    } else {
      this.list = $E('ul',this.container);
    }
    this.errorMessage = new Element('li',{
      'class': 'error'
    }).setHTML('Could not retrieve data');
    this.list.adopt(this.errorMessage);
  }
});
Ticker.implement(new Options);