ftp_rmdir() delete only empty folders...

if you want to delete the entire contents of a folder try its.

Exemple...

<?php
$ftp_server = "YourIP";
$ftp_user_name = "YourUsername";
$ftp_user_pass = "YourPassword";

// Connection
echo "Connecting to $ftp_server";
$conn_id = ftp_connect($ftp_server);
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);

//Enable PASV ( Note: must be done after ftp_login() )
ftp_pasv($conn_id, true);

// check connection
if((!$conn_id) || (!$login_result)){
    die("FTP connection has failed !");
}
echo "<br/>Login Ok.";

// Function to delete an entire folder
function ftp_rrmdir($conn_id, $directory){
    $lists = ftp_mlsd($conn_id, $directory);
    unset($lists[0]);
    unset($lists[1]);

    foreach($lists as $list){
        $full = $directory . '/' . $list['name'];

        if($list['type'] == 'dir'){
            ftp_rrmdir($conn_id, $full);
        }else{
            ftp_delete($conn_id, $full);
        }
    }

    ftp_rmdir($conn_id, $directory);
    return true;
}

//Now run ftp_rrmdir()
if(ftp_rrmdir($conn_id, 'YOUR/PATH/')){
    echo = "Folder deleted !";
}

//close
ftp_close($conn_id);

?>

Please note that this function, like rmdir, requires that the directory be empty.