Newbie having Trouble - Error #1009

programming flash
1

I am new to Flash and am working on a banner slider where there are 5 different images (slides) that come onto the scene about 8 seconds apart. Each slide I am trying to link to a web page but am getting the error; TypeError: Error #1009: Cannot access a property or method of a null object reference.
at NLE_fla::MainTimeline/frame1()

I’m sure it has to do with the link on the second slide not being found since the slide doesn’t load right away. Am I supposed to be loading some variables first or something? Here’s my code;

slide_btn1.addEventListener(MouseEvent.CLICK, fl_ClickToGoToWebPage1);

function fl_ClickToGoToWebPage1(event:MouseEvent):void
{
navigateToURL(new URLRequest(“http://www.adobe.com”), “_blank”);
}

slide_btn2.addEventListener(MouseEvent.CLICK, fl_ClickToGoToWebPage_2);

function fl_ClickToGoToWebPage_2(event:MouseEvent):void
{
navigateToURL(new URLRequest(“http://www.adobe.com”), “_blank”);
}