NFS problem on W2003 using SFU

Hi,

I'm having problems getting a brand new HP NAS 2000s box to work from
a Solaris 8 box.

In the following environment, it works fine:

Stand alone Unix (Solaris 8) server using local accounts (no NIS).
NAS entry in /etc/hosts, with NAS referenced for file system mount via
hostname.
Stand alone NAS (W2003) server using local accounts.
/etc/passwd and /etc/group files copied onto NAS and account mapping
set up.
Stand alone PC (W2K) client accessing NAS with local accounts.
A single share for both PC and Unix to access, with a single user
access permissions on the share and file system (mapped from Unix to
PC user account and using the same name).

But when I move the NAS into an Active Directory along with the client
PC's, it all goes pear shaped for the Unix servers.

Stand alone Unix server using local accounts.
NAS entry in /etc/hosts both for hostname (friendly) and FQDN (taken
from AD), with NAS referenced for file system mount via FQDN.
NAS server using AD accounts.
/etc/passwd and /etc/group files copied onto NAS and account mapping
set up against AD.
PC (W2K) client accessing NAS with AD accounts.
A single share for both PC and Unix to access, with a single user
access permissions on the share and file system (mapped from Unix to
AD user account and using the same name).

Once I move the NAS and the clients into the Active Directory, the PC
clients have no problem accessing the NAS share, but the Unix boxen
can not access it at all and get lots and lots of NFS & RPC errors.
Below is an extract from the /var/adm/messages file showing the errors
I was getting.

====
Aug 16 17:17:10 unix_server last message repeated 3 times
Aug 16 17:17:14 unix_server nfs: [ID 664466 kern.notice] NFS setattr
failed for server nas_box: error 7 (RPC: Authentication error)
Aug 16 17:17:14 unix_server last message repeated 1 time
Aug 16 17:17:15 unix_server nfs: [ID 664466 kern.notice] NFS lookup
failed for server nas_box: error 7 (RPC: Authentication error)
Aug 16 17:17:20 unix_server last message repeated 7 times
Aug 16 17:17:34 unix_server nfs: [ID 664466 kern.notice] NFS access
failed for server nas_box: error 7 (RPC: Authentication error)
Aug 16 17:17:34 unix_server last message repeated 1 time
Aug 16 17:17:34 unix_server nfs: [ID 664466 kern.notice] NFS read
failed for server nas_box: error 7 (RPC: Authentication error)
Aug 16 17:17:35 unix_server last message repeated 2 times
Aug 16 17:17:45 unix_server nfs: [ID 664466 kern.notice] NFS setattr
failed for server nas_box: error 7 (RPC: Authentication error)
Aug 16 17:17:45 unix_server last message repeated 1 time
====

Any and all suggestions / comments appreciated!
Julian.