Не работает header() после размещения сайта на сервере

<link rel="stylesheet" type="text/css" href="css/style.css">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<?php
require_once 'mysql_login.php';
session_start();
error_reporting(E_ALL);
ini_set('display_errors', 1);
 
echo <<<END
<div class="admin_login">
    <form name="authorization" action = "login.php" method = "post">
        <div class="admin_login_element">
            <p>Login:</p>
        </div>
        <div class="admin_login_element">
            <input type="text" size="15" name="name">
        </div>
        <div class="admin_login_element">
            <p>Password:</p>
        </div>
        <div class="admin_login_element">
            <input type="password" size="15" name="password">
        </div>
        <input type="submit" name = "enter" value="Войти" class="login_button">
    </form>
</div>
END;
if (isset($_POST['password']) && ($_POST['name'] == 'admin'))
{  
    $password = md5($_POST['password']);
    
    $query  = mysql_query("SELECT `iduser` FROM `user` WHERE password = '$password'");
    $iduser = mysql_fetch_row($query);
    
    if ($iduser[0])
    {
        $_SESSION['admin'] = $iduser[0];
        header("Location: admin.php");
    }
}
?>

<?php
session_start();
require_once 'mysql_login.php';
error_reporting(E_ALL);
ini_set('display_errors', 1);
 
if (isset($_POST['password']) && ($_POST['name'] == 'admin'))
{  
    $password = md5($_POST['password']);
    
    $query  = mysql_query("SELECT `iduser` FROM `user` WHERE password = '$password'");
    $iduser = mysql_fetch_row($query);
    
    if ($iduser[0])
    {
        $_SESSION['admin'] = $iduser[0];
        header("Location: admin.php");
    }
}
 
echo <<<END
 
<link rel="stylesheet" type="text/css" href="css/style.css">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<div class="admin_login">
    <form name="authorization" action = "login.php" method = "post">
        <div class="admin_login_element">
            <p>Login:</p>
        </div>
        <div class="admin_login_element">
            <input type="text" size="15" name="name">
        </div>
        <div class="admin_login_element">
            <p>Password:</p>
        </div>
        <div class="admin_login_element">
            <input type="password" size="15" name="password">
        </div>
        <input type="submit" name = "enter" value="Войти" class="login_button">
    </form>
</div>
END;
?>

<link rel="stylesheet" type="text/css" href="css/style.css">
<?php
session_start();
if (isset($_POST['exit']))
{
    session_destroy();
    header("Location: login.php");
}
?>
<?php if ($_SESSION['admin']): ?>
<div class="admin_header">
    <form name="exit" action = "admin.php" method = "post">
        <input type="submit" name = "exit" value="Выйти">
    </form>
</div>
<div class="user">
    <div class="user_main">
        <form method="post" action="user_handler.php">
<?php include "user_handler.php"; ?>
            <input type="submit" name="delete" value="Удалить">
        </form>
    </div>
</div>
<div class="post_right">
    <div class="user_main">
<?php include "post_handler.php"; ?><br>
    <form method="post" action="post_handler.php">
        <input type="text" name="title" size="50">
        <textarea name="post" cols="40" rows="20"></textarea>
        <input type="submit" name="add" value="Добавить">
    </form>
    </div>
</div>
 <?php else: header("Location: login.php"); ?>
 <?php endif; ?>

error_reporting(E_ALL);

ini_set('display_errors', 0))

error_log()