A chi interessasse questa è la soluzione


import flash.net.FileReference;

var listener:Object = new Object();

listener.onSelect = function(file:FileReference):Void {
trace("onSelect: " + file.name);
}
listener.onCancel = function(file:FileReference):Void {
trace("onCancel");
}
listener.onOpen = function(file:FileReference):Void {
trace("onOpen: " + file.name);
}
listener.onProgress = function(file:FileReference, bytesLoaded:Number, bytesTotal:Number):Void {
trace("onProgress with bytesLoaded: " + bytesLoaded + " bytesTotal: " + bytesTotal);
}
listener.onComplete = function(file:FileReference):Void {
trace("onComplete: " + file.name);
}
listener.onIOError = function(file:FileReference):Void {
trace("onIOError: " + file.name);
}

pulsante_btn.onRelease = function() {
fileRef = new FileReference();
fileRef.addListener(listener);
var url:String = "http://www.mioSito.com/immagini/fotograndi/imm1.jpg";
if(!fileRef.download(url, "imm1.jpg")) {
trace("dialog box failed to open.");
}

}