TypeError: Error #1009:

I am trying to make a eccomerce header with rotating images that are linked in flash CS4. My problem is i get this error #1009 and im not sure why. btn1 works fine but btn2 says its nul and i check spelling and its correct for my instnace for button. it is the same for btn3-5 with the error.

btn1.addEventListener(MouseEvent.MOUSE_UP, goLayersSite);

function goLayersSite(event:MouseEvent):void {
     var slideShow1:URLRequest = new URLRequest ("http://www.URL.com");
     navigateToURL(slideShow1);
}

btn2.addEventListener(MouseEvent.MOUSE_UP, goLayersSite01);

function goLayersSite01(event:MouseEvent):void {
     var slideShow2:URLRequest = new URLRequest ("http://www.url.com");
     navigateToURL(slideShow2);
}

btn3.addEventListener(MouseEvent.MOUSE_UP, goLayersSite02);

function goLayersSite02(event:MouseEvent):void {
     var slideShow3:URLRequest = new URLRequest ("http://www.url.com");
     navigateToURL(slideShow3);
}

btn4.addEventListener(MouseEvent.MOUSE_UP, goLayersSite03);

function goLayersSite03(event:MouseEvent):void {
     var slideShow4:URLRequest = new URLRequest ("http://www.url.com");
     navigateToURL(slideShow4);
}

btn5.addEventListener(MouseEvent.MOUSE_UP, goLayersSite04);

function goLayersSite04(event:MouseEvent):void {
     var slideShow5:URLRequest = new URLRequest ("http://www.url.com");
     navigateToURL(slideShow5);
}