Wat doe ik verkeerd

<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) {
session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
$_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['Username'])) {
$loginUsername=$_POST['Username'];
$password=$_POST['password'];
$MM_fldUserAuthorization = "";
$MM_redirectLoginSuccess = "/login/login.php";
$MM_redirectLoginFailed = "/index.php";
$MM_redirecttoReferrer = false;
mysql_select_db($database_website, $website);

$LoginRS__query=sprintf("SELECT username, password FROM login WHERE username=%s AND password=%s",
GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));

$LoginRS = mysql_query($LoginRS__query, $website) or die(mysql_error());
$loginFoundUser = mysql_num_rows($LoginRS);
if ($loginFoundUser) {
$loginStrGroup = "";

//declare two session variables and assign them
$_SESSION['MM_Username'] = $loginUsername;
$_SESSION['MM_UserGroup'] = $loginStrGroup;

if (isset($_SESSION['PrevUrl']) && false) {
$MM_redirectLoginSuccess = $_SESSION['PrevUrl'];
}
header("Location: " . $MM_redirectLoginSuccess );
}
else {
header("Location: ". $MM_redirectLoginFailed );
}
}
?>

deze fout melding krijg ik. Ik gebruik dreamweaver. let niet op backticks etc.


Warning: mysql_select_db(): supplied argument is not a valid MySQL-Link resource in /home/koksnl/domains/koksgevraagd.nl/public_html/index.php on line 19

Fatal error: Call to undefined function GetSQLValueString() in /home/koksnl/domains/koksgevraagd.nl/public_html/index.php on line 22
Normaal moet alles werken als je een login script maakt in dreamweaver.