Flex Facebook API Callback

does anybody know what are the properties of the fail object parameter in the callback function for flex facebook Graph API 1.7 ?

private function onLogin(response:Object, fail:Object):void
{
    if (fail) {
        // How do I check the message here?
    }开发者_如何学Go
}

You can see all properties of an object by the following loop.

for(var id:String in fail) {
   var value:Object = fail[id];

   trace(id + " = " + value);
}