upload molteplici files in php

[Maxiv]

Hai ragione tu, effettivamente mancava il trattino in form-data.
ora mi da questo errore:
Warning: move_uploaded_file() expects parameter 1 to be string, array given in D:\inetpub\webs\public\upload.php on line 8
Upload NON valido!
PHP

<?php
$uploaddir = 'D:/inetpub/webs/public/prodotti/';
$userfile_tmp = $_FILES['userfile']['tmp_name'];
$userfile_name = $_FILES['userfile']['name'];
foreach($_FILES as $key=>$file){
    $userfile_tmp = $_FILES[$key]['tmp_name'];
    $userfile_name = $_FILES[$key]['name'];
    if (move_uploaded_file($userfile_tmp, $uploaddir . $userfile_name)) {
          echo 'File inviato con successo.';
    }
    else{
          echo 'Upload NON valido!';
    }
}
//header("location: /gestione/login_prodotti.asp");
?>