Ciao cosi dovrebbe andare
codice:
<?php
session_start();
if(isset($_SESSION['ID_cliente'])){
	require_once("../amministra/config.php");
	$documento=mysql_fetch_array(mysql_query("SELECT * FROM immagini WHERE ID = '$_GET[id]'"));
	if($_GET['lang']=='it'){$file_download=$documento['file'];}
	mysql_close($link);
	    $mime_types = array(
        "bmp" => "image/bmp",
        "exe" => "application/octet-stream",
        "html" => "text/html",
        "ico" => "image/x-icon",
        "jpeg" => "image/jpeg",
        "png" => "image/png",
        "jpg" => "image/jpeg",
        "mov" => "video/quicktime",
        "mp3" => "audio/mpeg",
        "mp4" => "video/mpeg",
        "mpeg" => "video/mpeg",
        "mpg" => "video/mpeg",
        "txt" => "text/plain",
        "wav" => "audio/x-wav",
        "zip" => "application/zip"
     );
	 
	$file='../images/documenti/'.$file_download;
	$info  = pathinfo($file);
    $ext = strtolower($info["extension"]);
    $mt = isset($mime_types[$ext]) ? $mime_types[$ext] : "application/octet-stream";
	//exit();
	//header("Content-type:*");
	header("Cache-Control: public");
	header("Content-Type: {$mt}");
        header("Content-Description: File Transfer");
	header("Content-Disposition: attachment; filename=".$file);
	header("Content-Transfer-Encoding: binary");
	readfile($file);
	exit();
}
?>
Saluti
Davide