Live Chat - Custom WordPress Install

I receive a 404 error when I click on the Add Chat button on the Page/Post editor via wp-admin.

This is a custom wordpress installation.

Directory structure
- wp-config.php
- index.php
-- cms < core wordpress files
-- content < plugins, themes, uploads

I define the location of wordpress content via wp-config. Here's what it looks like.

if ( !defined('ABSPATH') )
define('ABSPATH', dirname(__FILE__) . '/cms/');

require_once(dirname(__FILE__) . '/db-config.php');

define('WP_CONTENT_DIR', realpath(ABSPATH.'../content/'));

define('WP_HOME', 'http://' . $_SERVER['HTTP_HOST']);
define('WP_SITEURL', 'http://' . $_SERVER['HTTP_HOST'] . '/cms');
define('WP_CONTENT_URL', 'http://' . $_SERVER['HTTP_HOST'] . '/content');

Here's a full write up of how I set up this install. We use if for all our wordpress installations as we rely on svn externals and capistrano for deployment.