Reusing an object/variable name

Hello again!
Out of some curiosity and the use of possible standard key variables so I don’t have to create several instances to the same class, I was trying the following:

var urlRequest:URLRequest = new URLRequest(website + "/news_test.txt");
var urlLoader:URLLoader = new URLLoader();
var urlVars:URLVariables = new URLVariables();

urlRequest.method = URLRequestMethod.POST;
urlLoader.addEventListener(Event.COMPLETE, newsLoaded);

// First use of Request/Loader
function newsLoaded(event:Event):void {

// Second use
loginButton.addEventListener(MouseEvent.CLICK, loginOnClick, false, 0, true);
function loginOnClick(event:MouseEvent):void{
    urlVars.u = usernameTextField.text;
    urlVars.p = passwordTextField.text;
    urlRequest = new URLRequest("validate.asp"); // Does not work. = urlVars;
    urlLoader.load(urlRequest);  // Does not work.
    urlLoader.addEventListener(Event.COMPLETE, loginLoaded);

That approach gave me the following error:

Error:[Error #2101: The String passed to URLVariables.decode() must be a URL-encoded query string containing name/value pairs](
    at Error$/throwError()

This error does not occur if I try the same thing but instead of reusing urlRequest and urlLoader I create new instances of the same classes.
My question is:**
Is there a better approach to this on AS3? Something tells me I’m just heading the wrong way there…