[Erro ao logar]

<?php

//If the user has submitted the form
if($_POST['submit']){
//protect the posted value then store them to variables
$username = protect($_POST['username']);
$password = protect($_POST['password']);

//Check if the username or password boxes were not filled in
if(!$username || !$password){
//if not display an error message
echo "<center>You need to fill in a <b>Username</b> and a <b>Password</b>!</center>";
}else{
//if the were continue checking

//select all rows from the table where the username matches the one entered by the user
$res = mysql_query("SELECT * FROM `users` WHERE `username` = '".$username."'");
$num = mysql_num_rows($res);

//check if there was not a match
if($num == 0){
         //if not display an error message
         echo "<center>The <b>Username</b> you supplied does not exist!</center>";
}else{
         //if there was a match continue checking

         //select all rows where the username and password match the ones submitted by the user
         $res = mysql_query("SELECT * FROM `users` WHERE `username` = '".$username."' AND `password` = '".$password."'");
         $num = mysql_num_rows($res);

         //check if there was not a match
         if($num == 0){
         //if not display error message
         echo "<center>The <b>Password</b> you supplied does not match the one for that username!</center>";
         }else{
         //if there was continue checking

         //split all fields fom the correct row into an associative array
         $row = mysql_fetch_assoc($res);

         //check to see if the user has not activated their account yet
         if($row['active'] != 1){
         //if not display error message
         echo "<center>You have not yet <b>Activated</b> your account!</center>";
         }else{
         //if they have log them in

         //set the login session storing there id - we use this to see if they are logged in or not
         $_SESSION['uid'] = $row['id'];
         //show message
         echo "<center>You have successfully logged in!</center>";

         //update the online field to 50 seconds into the future
         $time = date('U')+50;
         mysql_query("UPDATE `users` SET `online` = '".$time."' WHERE `id` = '".$_SESSION['uid']."'");

         //redirect them to the usersonline page
         header('Location: ../reg/regusersOnline.php');
         }
         }
}
}
}

?>
<form action="../index.php" method="post">
<div id="border">
<table cellpadding="2" cellspacing="0" border="0">
         <tr>
         <td>Username:</td>
         <td><input type="text" name="username" /></td>
         </tr>
         <tr>
         <td>Password:</td>
         <td><input type="password" name="password" /></td>
         </tr>
         <tr>
         <td colspan="2" align="center"><input type="submit" name="submit" value="Login" /></td>
         </tr>
         <tr>
         <td align="center" colspan="2"><a href="./reg/register.php">Register</a> | <a href="./reg/forgot.php">Forgot Pass</a></td>
         </tr>
</table>
</div>
</form>
<?
ob_end_flush();
?>