Domain Mapping not in the SubSite's Tools menu

Hi Folks, I am not seeing the Domain Mapping menu item in the sub-site's Tools Menu. The network tools are there, and I have added and verified the ip address. In the Network adim:sites list, I see the space for Mapped Domain, but it is empty ('cause we cannot get to the place to add a domain).

Any ideas on where to start looking for the problem?

Thank you in advance.