header location - chyba

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

?> 


<? ob_start();  

if($_SESSION['login']!=""){
echo "přihlašen jako admin<br/>";
  }  
  else {

?>
<form action="login.php?login=1" method="post">      
Nick:  <input type="text" name="nick" value="" size="25" tabindex="1" />
Heslo: <input type="password" name="pass" value="" size="25" tabindex="2" />
       <input type="submit" name="submit" value="Přihlásit se" />
</form>
<?

  }
  
  $login = $_GET["login"];
  
if($login == "1"){
        $login = mysql_real_escape_string($_POST["nick"]);
        $pass = mysql_real_escape_string($_POST["pass"]);
        $md5pass = md5($pass);

        $dotaz = mysql_query("select * from user where login = '".mysql_real_escape_string($login)."' and pass = '".mysql_real_escape_string($md5pass)."'");
        $overeni = mysql_num_rows($dotaz);
        $row = mysql_fetch_array($dotaz);
        if($overeni == 1) {

        $_SESSION['login'] = stripslashes($login);
        $_SESSION['id'] = $row["id"];
        header("location: admin"); 
        die();
         } else {
    echo"Zadal jsi špatný login nebo heslo!";
}
}

$obsah= ob_get_clean(); 
require_once "theme.php";
?>
</body>
</html> 
<?
?>