Loader class problem loading swf

programming flash
1

I am trying to write a simple action to get a button to load an eternal swf onto the stage, or preferably into a target movie clip. My current understanding of what is needed to accomplish this is as follow:

  1. create a new Loader
  2. Create an even listener for each button to catch the Mouse.CLICK and run custom function.
  3. Create a new URLRequest and Loader load the URLrequest. (I am trying to apply this to each button so they will load unique swf’s)
  4. Have the stage addChild of my Loader.

This is what I have for that so far:

stop();

home_btn.addEventListener(MouseEvent.CLICK, home_btnclick)

function home_btnclick(e:MouseEvent):void
{
    var loader_mc : Loader = new Loader();
      var urlRequest : URLRequest = new URLRequest("home.swf");
      loader_mc.load(urlRequest);
      addChild(loader_mc);
}
portfolio_btn.addEventListener(MouseEvent.CLICK, portfolio_btnclick)

function portfolio_btnclick(e:MouseEvent):void
{
     var loader_mc : Loader = new Loader();
      var urlRequest : URLRequest = new URLRequest("portfolio.swf");
      loader_mc.load(urlRequest);
      addChild(loader_mc);
}
contact_btn.addEventListener(MouseEvent.CLICK, contact_btnclick)

function contact_btnclick(e:MouseEvent):void
{
     var loader_mc : Loader = new Loader();
      var urlRequest : URLRequest = new URLRequest("contact.swf");
      loader_mc.load(urlRequest);
      addChild(loader_mc);
}

When I preview my project an error is returned :

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at EclipticVisualsindex_fla::MainTimeline/frame61()

My guess is that the external swf has not been loaded before it has been called? Any help on this will be greatly appreciated! Thanks!!