Can't add Domain Admins from Parent into Child Domain

Conaway · Guest

I have a forest at Windows 2000 forest functional level. In the forest, I
have two domains at Windows 2003 domain functional level. I am unable to add
Domain Admins from parent.com into local Administrators group of
child.parent.com.

The only object types I can add from the parent domain are 'other objects'
and 'contacts', but not users or groups. I don't have problems adding domain
admins into the Administrators group between other domains in the same
forest, only the child domain is difficult.

I'm wonder if there is some breakdown in the transitive trust here?