I have a button that keeps blowing up my code

can someone take a look and tell me why? I have imported the classes

package {
import flash.display.MovieClip;
import flash.net.URLLoader;
import flash.net.URLRequest;
import flash.events.Event;
    import com.yahoo.astra.fl.controls.Tree; 
import com.yahoo.astra.fl.controls.treeClasses.*;
import flash.events.MouseEvent;
import fl.controls.Button;

public class VideoPlaylistNoThumb extends MovieClip {
  private var xmlLoader:URLLoader;
  public var btnNext:Button;
  //btnNext.label = "Next";
 
 
  public function VideoPlaylistNoThumb():void {
   // Load the playlist file, then initialize the media player.
   xmlLoader = new URLLoader();
   xmlLoader.addEventListener(Event.COMPLETE, initMediaPlayer);
   xmlLoader.load(new URLRequest("playlist2.xml"));
  }
 
  public function initMediaPlayer(event:Event):void {
   var myXML:XML = new XML(xmlLoader.data);
   var item:XML;
   for each(item in myXML.vid) { // populate playlist.
    // Send data to List.
    videoList.addItem({label:item.attribute("desc").toXMLString(),
    data:item.attribute("src").toXMLString(),
    data:item.attribute("id").toXMLString(),
    data:item.attribute("wNnext").toXMLString(),
    data:item.attribute("aNext").toXMLString(),
    data:item.attribute("allNext").toXMLString(),
    ttURL:item.attribute("ttURL").toXMLString()});
}  
   // Select the first video.
   videoList.selectedIndex = 0;
   myVid.autoRewind = true;
   // Listen for item selection.
   videoList.addEventListener(Event.CHANGE, listListener);
   // And automatically load it into myVid.
   myVid.source = videoList.selectedItem.data;
   myVidCaptioning.source = videoList.selectedItem.ttURL;
   myVidCaptioning.flvPlayback = myVid;
   // Pause video until selected or played.
   //myVid.pause();
}  

  // Detect when new video is selected, and play it
  function listListener(event:Event):void {
   myVid.stop();
   myVidCaptioning.source = event.target.selectedItem.ttURL;
   myVidCaptioning.showCaptions = false;
   myVidCaptioning.showCaptions = true;
   myVid.autoPlay = true;
   myVid.play(event.target.selectedItem.data);

  }
 
   function clickHandler(event:MouseEvent):void {
      trace("I have been clicked");
  }

  btnNext.addEventListener(MouseEvent.CLICK, clickHandler); 

}

}

It is not recognizing btnNext