Password Protected and Private Pages/Posts Return 403 Error

I’ve just tried to create a password protected page but I only get 403 Forbidden errors when trying to access or preview them. Is this an .htaccess problem? My wordpress installation is in a subdirectory, so perhaps that is the cause?

My .htaccess file is as follows:

AddType x-mapp-php5 .php
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

My index.php for displaying wordpress sub:

<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require('./_fmdgwp/wp-blog-header.php');
?>

I tried the ErrorDocument handling addition to the .htaccess:

ErrorDocument 401 /401.html
ErrorDocument 403 /403.html

But that didn’t work either.

Any help would be awesome. Thanks!