Win 2003 networking issue

I have a WIn 2003 server DC in a Child domain a.b.lan and
I can not connect to any of my client machines by doing a
\\<computer_name>. I keep getting a \\<computer_name> is
not accessible. You might not have permissions to use
this network resource. Contact the administrator for the
server to find out if you have access permissions. The
account is not authorized to log in from this station.

I can connect to the Root DC which is in b.lan, but non
of it's clients shares as well.

Netbios over TCP/IP is enabled and my computer browser is
started on the server. From the Root DC I can connect to
any machine in either domain.

HELP!!!!!!