Sending variables from Flash to php and back to Flash

programming flash
1

I am trying to send two String variables to php and from php back to Flash where i am trying to display them in TextField. The problem is that i keep geting this error:

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

Here is my AS3 code:

var request:URLRequest = new URLRequest ("http://localhost/addUser.php");
request.method = URLRequestMethod.POST;
                
var variables:URLVariables = new URLVariables();
                
variables.firstName = "FirstName";
variables.lastName = "LastName";            
request.data = variables;
                
var loader:URLLoader = new URLLoader (request);
loader.addEventListener(Event.COMPLETE, onComplete);
loader.dataFormat = URLLoaderDataFormat.VARIABLES;
loader.load(request);
                
        
public function onComplete (event:Event):void{
statusTxt1.text = event.target.data;
}

And my addUser.php code:

<?php

$fname = $_POST['firstName'];
$lname = $_POST['lastName'];

echo $fname;

?>

Can someone please help me on this?

thanks in advance,
cheers