throw new Sprite()

		 function uncaughtErrorHandler(event:UncaughtErrorEvent):void
         {
             var message:String;
             
             if (event.error is Error)
             {
                 message = Error(event.error).message;
             }
             else if (event.error is ErrorEvent)
             {
                 message = ErrorEvent(event.error).text;
             }
             else
             {
                 message = event.error.toString();
             }
         }

		 function uncaughtErrorHandler(event)
         {
             var message; // String
             
             if (event.error.message) // It's an Error object
             {
                 message = event.error.message;
             }
             else if (event.error.text) // It's an ErrorEvent object
             {
                 message = event.error.text;
             }
             else
             {
                 message = event.error.toString();
             }
         }

package
{
    import flash.display.Sprite;
    import flash.events.ErrorEvent;
	import flash.events.MouseEvent;
	import flash.events.UncaughtErrorEvent;

    public class UncaughtErrorEventExample extends Sprite
    {
        public function UncaughtErrorEventExample()
        {
            loaderInfo.uncaughtErrorEvents.addEventListener(UncaughtErrorEvent.UNCAUGHT_ERROR, uncaughtErrorHandler);
			
			drawUI();
        }
		
        private function uncaughtErrorHandler(event:UncaughtErrorEvent):void
        {
            if (event.error is Error)
            {
                var error:Error = event.error as Error;
				// do something with the error
            }
            else if (event.error is ErrorEvent)
            {
                var errorEvent:ErrorEvent = event.error as ErrorEvent;
				// do something with the error
            }
            else
            {
                // a non-Error, non-ErrorEvent type was thrown and uncaught
            }
        }
		
		private function drawUI():void
		{
			var btn:Sprite = new Sprite();
			btn.graphics.clear();
			btn.graphics.beginFill(0xFFCC00);
			btn.graphics.drawRect(0, 0, 100, 50);
			btn.graphics.endFill();
			addChild(btn);
			btn.addEventListener(MouseEvent.CLICK, clickHandler);
		}
		
		private function clickHandler(event:MouseEvent):void
		{
			throw new Error("Gak!");
		}
    }
}

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009" 
    				   xmlns:s="library://ns.adobe.com/flex/spark" 
					   xmlns:mx="library://ns.adobe.com/flex/halo"
                       applicationComplete="applicationCompleteHandler();">
    
    <fx:Script>
        <![CDATA[
		    import flash.events.ErrorEvent;
			import flash.events.MouseEvent;
		    import flash.events.UncaughtErrorEvent;
            
			private function applicationCompleteHandler():void
            {
                loaderInfo.uncaughtErrorEvents.addEventListener(UncaughtErrorEvent.UNCAUGHT_ERROR, uncaughtErrorHandler);
            }
    
            private function uncaughtErrorHandler(event:UncaughtErrorEvent):void
            {
                if (event.error is Error)
                {
                    var error:Error = event.error as Error;
                    // do something with the error
                }
                else if (event.error is ErrorEvent)
                {
                    var errorEvent:ErrorEvent = event.error as ErrorEvent;
                    // do something with the error
                }
                else
                {
                    // a non-Error, non-ErrorEvent type was thrown and uncaught
                }
            }
            
            private function clickHandler(event:MouseEvent):void
            {
                throw new Error("Gak!");
            }
        ]]>
    </fx:Script>
      
    <s:Button label="Cause Error" click="clickHandler(event);"/>
</s:WindowedApplication>

package
{
    import flash.display.Loader;
    import flash.display.Sprite;
	import flash.events.ErrorEvent;
	import flash.events.UncaughtErrorEvent;
	import flash.net.URLRequest;

    public class LoaderUncaughtErrorEventExample extends Sprite
    {
		private var ldr:Loader;
		
        public function LoaderUncaughtErrorEventExample()
        {
			ldr = new Loader();
			ldr.load(new URLRequest("child.swf"));
            ldr.uncaughtErrorEvents.addEventListener(UncaughtErrorEvent.UNCAUGHT_ERROR, uncaughtErrorHandler);
        }
		
        private function uncaughtErrorHandler(event:UncaughtErrorEvent):void
        {
            if (event.error is Error)
            {
                var error:Error = event.error as Error;
				// do something with the error
            }
            else if (event.error is ErrorEvent)
            {
                var errorEvent:ErrorEvent = event.error as ErrorEvent;
				// do something with the error
            }
            else
            {
                // a non-Error, non-ErrorEvent type was thrown and uncaught
            }
        }
    }
}