Code Not Working

[BellQuestWars]

Okay, This code isnt working:

 if (keyp == 56) {
p1y = -1; 
var url = 'update.php?X='+p1x+'&Y='+p1y;

var xhr = new XMLHttpRequest();
this.privates.xhr.open("GET", url, true);
xhr.send(null);
}  

This is the code that changes variables when the 8 key is pressed (up on the keypad) But for some reason, when the key is pressed, the players moves up, but nothing changes in the database.  Also if I go to the url mypage.com/update.php?x=3&y=3, it doesnt change the datbase.

Heres update.php:

session_start();
require_once("connect.php");
$x = $_GET[X];
$y = $_GET[Y];
mysql_query("UPDATE members SET x = '$x' WHERE username = '$_SESSION[username]'");
mysql_query("UPDATE members SET y = '$y' WHERE username = '$_SESSION[username]'");
?>

[BellQuestWars]

Okay, so I fixed the PHP script so that the page does change, it was a simple typo (should have been upercase X and Y in the adress bar...) But now I need to figure out the problem with the AJAX part...