Error message: Warning! Wildcard DNS for DOMAIN_CURRENT_SITE may not be configured correctly!

I am hosted on Dreamhost and have installed a WPMU installation at splendidwebsites.com.

I currently have the Multi-Domains plugin installed but it is not working correctly. The two domains configured are:

spendidwebsites.com (current domain site) and
splendidwebsite.com (a secondary multi-domain)

SYMPTOMS:

1) I have built a test site: http://23drft.splendidwebsite.com and the front end shows fine, but when I try to access the dashboard it won't authenticate with my Admin username and password.

2) Looking at the Settings for Multi-Domains: The base domain splendidwebsites.com is appearing as DOMAIN_CURRENT_SITE

3) I get an error message in the Settings for Multi-Domains that says:

Warning! Wildcard DNS for DOMAIN_CURRENT_SITE may not be configured correctly!

Unable to contact the random hostname (e4417a.DOMAIN_CURRENT_SITE).

4) The primary domain splendidwebsites.com, works perfectly both dashboard and front end.

CHECKS I HAVE ALREADY COMPLETED:

1. I have contacted Dreamhost and they tell me that the wildcard domain is definitely configured correctly on their side.

2. I have the following entries in my wp-config file:

define( 'SUNRISE', 'on' );
define('WP_DEBUG', false);
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', true);
define('DOMAIN_CURRENT_SITE', 'splendidwebsites.com');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);
/* That's all, stop editing! Happy blogging. */

What I'm hoping is that someone can give me an indication of what I'm missing and/or what I've done incorrectly in configuring this installation.

Many thanks in advance for your assistance.

Kind regards,
JAMES WILLIAMS