[Ionut]

You have entended the class as movieclip so you need to do an addchild method for the the instance of that class for it to be actually visible. You have in myItem.as the click method

// on click open the url
public function onMouseUp(event:Event)
{
     var URLNavigator:URLNav = new URLNav(_url, _target);
     URLNavigator.callLink();

     // since you modified the class to be a movieclip
     // add to whatever movieclip you want to use as a holder

     stage.addChild(URLNavigator)

    // or whatever holder movieclip

    holderMc.addChild(URLNavigator);
			
}

Cheers,
Ionut.