ErrorEvent  - AS3

package {
    import flash.display.Sprite;
    import flash.net.URLLoader;
    import flash.net.URLRequest;
    import flash.events.*;

    public class ErrorEventExample extends Sprite {
        private var loader:URLLoader;
        private var request:URLRequest;
        
        public function ErrorEventExample() {
            loader = new URLLoader();
            loader.addEventListener(IOErrorEvent.IO_ERROR, errorHandler);
            loader.addEventListener(SecurityErrorEvent.SECURITY_ERROR, errorHandler);

            request = new URLRequest();
            loadFromFileSystem();
        }
        
        private function loadFromFileSystem():void {
            request.url = "MissingFile.xml";
            loader.load(request);
        }

        private function loadFromNetwork():void {
            request.url = "http://www.[yourDomain].com/MissingFile.xml";
            loader.load(request);
        }
        
        private function errorHandler(event:ErrorEvent):void {
            trace("errorHandler: " + event);
            if(event is IOErrorEvent) {
                loadFromNetwork();
            }
        }
    }
}