In using the 'Add Virtual Site' interface, I had entered blah as the 'Host Name' and test.com as the 'Domain Name'. In trying to add this second one, I attempted to add blah2 as the 'Host Name' and test.com as the 'Domain Name' and received the following error message "Another site is already aliased to the domain test.com".
In the "site settings" configurations for that second domain, is "web access by domain" checked? If so, uncheck it. You can only have one web site answer for the domain -- e.g. blah.test.com answers for test.com.
Alfredo -- People-Link/Institute for Mass Communications www.people-link.org Communications for a Better World...and for the People Who are Building One! Members, Local 1180, Communications Workers of America, AFL-CIO