Can't map a domain to a subsite

Hi, I have the domain http://www.whitehatwiki.biz pointing to our server ip (67.192.247.160).
I want to use it as top level domain for http://wikipediaexperts.buzzr.com, but when I come to domain mapping option inside the subsite it tells me the top level domain is not well configured, however if you do a dns lookup for it, you'll see that's pointing correctly.

Can you help?