[ActiveDir] RPC error when trying to add higher level domain groups to local admin groups on servers

[Washington, Booker]

I am a child domain of an empty root (sample.com)   My domain is Mgt.sample.com; there are other domains in the forest coe.sample.com, cc.sample.com, etc     Whenever I try to add either domain admins or enterprise admins (from the other domains...(And even other "Groups" to the local admin group for one of my servers, the following things seem to happen   1.    When I try to access sample.com or other domains in the forest, it takes forever (5 minutes or so) for the domain to be contacted   2.    Once contacted, if I try to add the group, I get the following error               Windows cannot process the object with the name "Domain admins" because of the following error: RPC server is unavailable   You can insert any group between the " ".    User accounts seem to add ok, but group accounts, no luck.   Any ideas   I am suspecting, domain replication/global catalog issues, maybe?   Thanks