Domain mapping redirect mapped domain to home page

Hey,

I am managing a multisite install at garethsworld.com. I have installed the domain mapping plugin and I am trying to assig the domain name catstogo.org.nz to the subdomain site garethsworld.com/catstogo. I have followed all instructions but at the moment i seem to get redirected to the home page. Not sure where i am going wrong. can i please get some help?

Cheers