When it asked you for the administrator's user name... did you just type in "administrator"?

I don't know about that particular tool, so this is just a stab in the dark. But sometimes, on Windows systems, when dealing with cross-trust situations, you have to enter the name as "domainname\username" for it to work. Otherwise, it thinks you're talking about the local computer's user account, which is a different thing.

So, for instance, when it asks you for the domain administrator's user name, and your domain is called "foobar", then you sometimes have to enter: "foobar\Administrator" in order for it to work.

Again, this is just a stab in the dark as I haven't used that wizard tool.