The server is redirecting the request for this address in a way that will never complete

Other sites are working well with the domain mapping plugin. But, for this site http://naturebydesign.9thsites.com when I input naturebydesignnw.com into the plugin I get this error message:

The page isn't redirecting properly

Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

I have seen this in the forums before. But, where this is weird is that if I remove naturebydesignnw.com from the mapping plugin then naturebydesignnw.com actually gets you to the appropriate page. Except that naturebydesign.9thsites.com is showing in the address bar.