Domain Mapping -> redirecting to registration page. Help!

I installed the domain mapping according to instructions but I have a problem when I try to access the mapping domain or even the subdomain original, after I have mapped the domain - now when I try to access the blog through either of these directions, I am sent to the registration page and given the following information:

http://citylogica.com/wp-signup.php?new=mercedguide.com

>>>>
Greetings Site Administrator! You are currently allowing 'none' registrations. To change or disable registration go to your Options page.

Spam is a huge problem on the Internet. Protect your site by using WP-Hashcash, Cookies For Comments or follow this advice. They should help stop or slow down those who create spam blogs on your site.
>>>>>

Note - when I delete the mapping for this blog's URL, I can once again access the blog via the subdomain (merced.citylogica.com).

Also, if I just remove domain mapping tool and specify the domain in the blog edit > site URL fields, it will also work to access it via the domain. In otherwords, access to the blog should technically work via subdomain *or* URL. But with the domain-mapping tool in place and the mapping in place, both stop working.

One thought - when I go to the admin options I notice the option for Support Only default to "yes" and even when I attempt to change it to "no" and submit... it still comes back as "yes". Perhaps this is related?

Any insights are appreciated.

Thanks!