'cannot yet handle MBCS in html_entity_decode' error on WP-DownloadManager

I am currently working on a WordPress-powered site. One of its features is a download section. After comparing some WordPress plugins, I decided to use Lester ‘GaMerZ’ Chan‘s WP-DownloadManager.
When I use that plugin on WordPress 2.5.1, I got an error. It’s something like this:

Warning: cannot yet handle MBCS in html_entity_decode()! in /home/.../wp-downloadmanager.php on line 308

Is it a bug? It seems that I got this error message because this plugin needs PHP 5 (I still use PHP 4). Since many hosts having PHP 5-enabled (even it does not always installed as the default version), it should not be that difficult to solve this issue. All I need to do is making all .php files are treated as PHP 5 files. Okey, this is a straight forward solution: add a new line in your .htaccess file. You should find it in your WordPress directory, if not, just add this line:

AddType application/x-httpd-php5 .php

And, the problem solved.
Update: Put AddType application/x-httpd-php5 .php in the first line in .htaccess file. Here is mine:

AddHandler application/x-httpd-php5 .php
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress

After that, create a new php file e.g. myphpinfo.php and include this line:

<?php phpinfo(); ?>

This will display about PHP version (affected by .htaccess).