sister site is getting a Domain unavailable mssg

The way we are setup.
both sites are running NAT.
Both sites use a firewall that is our router also (Netscreen). And we are still using NT 4 as controllers.
Problem:
User is able to login at point A but when same user tries to login at point B the user gets a domain unavailable message at point B and is unable to login. All workstations are WIN2K.
One other strange item is that on point B systems user profiles are change to unavailable.
We got one working by rejoining the system to the domain.