Hjälp!!!

Hej!
Jag håller på med en sida som man ska kunna logga in på ibland fungerar det men ibland inte. Varför?

login.php

<?php
include("config.inc.php");

session_start();
session_register('logedin');
session_register('username');

mysql_connect($database,$db_username,$db_password);
mysql_select_db($db);

$query = "SELECT password FROM users WHERE username='$name'";

$result = mysql_query($query);
$correctpassword = mysql_fetch_array($result);

if ($password==$correctpassword[0])
 {
  $logedin = true;
  $username = $name;

  $query = "UPDATE users SET status='online' WHERE username='$username'";
  $result = mysql_query($query);

  header("Location: main.php");
 }
else
 {
  $logedin = false;
  header("Location: error.php?id=wrong_password");
 }
?>

main.php

<?php
include("config.inc.php");

session_start();
#session_register('logedin');
#session_register('username');

if ($logedin==false)
 header("Location: error.php?id=wrong_password");

mysql_connect($database,$db_username,$db_password);
mysql_select_db($db);

$query = "SELECT name FROM users WHERE username='$username'";

$result = mysql_query($query);
$info = mysql_fetch_array($result);

?>

osv...

man blir skickad till error.php?id=wrong_password ifrån main.php sidan.