Help handling URLloader error

Hi I am trying to implement some error handling into my code.
I am still getting the error:
Error #2044: Unhandled IOErrorEvent:. text=Error #2035: URL Not Found.

I want to be able to feed invalid URLs into the loader without it causeing a problem.

Here is the relevant (?) extract of my code:

  var image_url = kanaImages[imageCount][email protected];
  image_loader = new Loader();
  image_loader.addEventListener(IOErrorEvent.IO_ERROR, catchIOError);
  image_loader.load(new URLRequest(image_url));
  image_loader.contentLoaderInfo.addEventListener(Event.COMPLETE, imageLoaded);
 private function catchIOError(event:IOErrorEvent)
  trace("Error caught: "+event.type); // this never gets triggered.

This works fine with valid URLs.

I was trying to do as Senocular describes here:

Thank you for taking the time to look at this problem!