permasalahan php?

tulisan errornya gimana?

ini gan, session ngga muncul sedangkan ini, kalau

$_SESSION-nya dikasih @ jadi @$_SESSION[]

@ahmadhanaf jd gini bukan?

 <?php
include('koneksi.php');
session_start();
if (isset($_POST['login'])) {
    $user = mysql_real_escape_string(htmlentities($_POST['username']));
    $pass = mysql_real_escape_string(htmlentities($_POST['password']));

    $sql = mysql_query("SELECT * FROM user WHERE username='$user' AND password='$pass'") or die(mysql_error()); //simpan variabel pilih user
    if (mysql_num_rows($sql) == 0) { //jika tidak ditemukan
        echo '<script language="javascript">alert("User tidak ada!"); document.location="index.php";</script>';
    } else { //jika ditemukan
        $row = mysql_fetch_assoc($sql);
        if ($row['level'] == 1) { // admin berdasarkan level, jika level 1 berarti admin
            @$_SESSION['pegawai'] = $user;
            @$_SESSION['nip'] = $row['nip'];
            @$_SESSION['nama'] = $row['nama'];
            echo '<script language="javascript">alert("Anda berhasil Login Pegawai!"); document.location="pegawai/index.php";</script>';
        } else {
            if ($row['level'] == 2) {
                @$_SESSION['penilai'] = $user;
                @$_SESSION['nip'] = $row['nip'];
                @$_SESSION['nama'] = $row['nama']; //berdasarkan kolom user
                echo '<script language="javascript">alert("Anda berhasil Login Sebagai penilai!"); document.location="penilai/index.php";</script>';
            }
            if ($row['level'] == 3) {
                @$_SESSION['atasan'] = $user;
                @$_SESSION['nip'] = $row['nip'];
                @$_SESSION['nama'] = $row['nama']; //berdasarkan kolom user
                echo '<script language="javascript">alert("Anda berhasil Login Sebagai atasan!"); document.location="atasan/index.php";</script>';
            }
        }
    }
}
?>

Iya gan, silahkan dicoba