codice:
<?php 
//
// Copyright 2001 Xavier Media Group
// http://www.xaviermedia.com/php/
//
// If you need help or have suggestions, please visit
// http://www.xaviermedia.com/forum/index.php or
// http://www.xaviermedia.com/php/password.phtml
//
if(!isset($_SERVER['PHP_AUTH_USER'])) 
{
	Header("WWW-Authenticate: Basic realm=\"Xavier Protection\""); 
	Header("HTTP/1.0 401 Unauthorized"); 
	echo "Text to send if user hits Cancel button\n"; 
	exit; 
} 
else
{
	$user_passwords = array (
		// user1 is the login name and password1 
		// is that users password. Add as many
		// lines as you like.
		"user1" => "password1", 
		"user2" => "password2",
		"user3" => "password3",
		"user4" => "password4"
		);

	if (($_SERVER['PHP_AUTH_USER'] == "") || ($_SERVER['PHP_AUTH_PW'] == ""))
	{
		Header("HTTP/1.0 401 Unauthorized"); 
		echo "Sorry, could find your password!";
		exit;
	}
	else if (strcmp($user_passwords  $_SERVER['PHP_AUTH_USER'],$_SERVER['PHP_
AUTH_PW'] ) == 0)
	{
		// This is the page that should be password protected.
		echo "This is the password protected page.";
		exit;
	}
	else
	{
		Header("HTTP/1.0 401 Unauthorized"); 
		echo "Sorry, could find your password!";
		exit;
	}
} 
?>
prova così...avevi dimenticato una sostituzione...