Error #1023: Incompatible override

override protected function draw(event:Event = null):void {
ReferenceError: Error #1065: Variable ClockTest is not defined.

the code is from <<Advanced Actionscript 3.0 With Design Patterns>>


  /** 
  * 
  * ABSTRACT METHOD TO BE OVERRIDDIN 
  * 
  **/ 
  protected function draw(event:Event):void { 
 
                } 
 
 /** 
  * 
  * **OVERRIDE** METHOD 
  * 
  **/ 
  **override** protected function draw(event:Event = null):void { 
                         var time:Time = _data.time; 
 
                        // Set the rotation of the hands based on the time 
                         // values. 
                         _hourHand.rotation = 30 * time.hour + 30 * time.minute / 60; 
                         _minuteHand.rotation  = 6 * time.minute + 6 * time.second / 60; 
                         _secondHand.rotation = 6 * time.second; 
                 }

wondering any one can help? thanks.