Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\ag-ki\validateLogin.php on line 12

<?php
session_start();
require_once("connect.php");

$result = @mysql_query("SELECT username,password, FROM users");

$username = $_POST["username"];
$password = md5($_POST["password"]);

$_SESSION['loggedin'] = false;

while ($row = mysql_fetch_array($result) ) {

    if ( ($row["password"] == $password) && (strtoupper($row["username"]) == strtoupper($username))) {

       $_SESSION['loggedin'] = true;
       $_SESSION['username'] = $username;
       echo $result2;

       if($row["class"] == 'admin') {
             echo "you are an admin";
			 $_SESSION['class'] = 'admin';
             header("location:admin.php");
           }
       else if ($row["class"] == 'user') {
             echo "you are a user";
			 $_SESSION['class'] = 'user';
             header("location:index.php");
           }
    }
}

if ($_SESSION['loggedin'] == false) {
   include("index.php");
    echo "<h1 style='color:red;'><center>Login Failed!</center></h1>";

}

?>