PHP FTP ftp_nlist 不起作用，返回布尔值 false

I have a little problem with this pice of code. The script connects, but it wont give me the folders that are located in root ... i am missing something?

    $ftp_server = "ftp.something.com";
    $ftp_user = "user";
    $ftp_pass = "pass";

    // set up a connection or die
    $conn_id = ftp_connect($ftp_server) or die("Couldn't connect to $ftp_server"); 

    // try to login
    if (@ftp_login($conn_id, $ftp_user, $ftp_pass)) 
    {
        echo "Connected as $ftp_user@$ftp_server
";
    } 
    else 
    {
        echo "Couldn't connect as $ftp_user@$ftp_server
";
    }

    $contents = ftp_nlist($conn_id, ".");
    var_dump($contents);

    ftp_close($conn_id);  

    die;

输出

Connected as $ftp_user@$ftp_server;

和

boolean false

为什么不列出文件?

我可以用

  file_exists("ftp//user:pass@host.com") 

...但是简单的部分不是我想要的，我什么都学不会

// after ftp_login(...)
ftp_pasv($conn_id, true);