[Samba] Access denied to shares samba 3

[max]

Hi,
I have samba-3.0.23d-1tr on a trustix 3.0 system. 
This samba was joined to a win 2k3 domain and it works perfect for lot of
months.
Now I can access only to tmp share, and samba server is very slow to expose
all shares.
If I launch wbinfo -u or wbinfo -g, I still see the users/group from win2k3
server, 
but in the log of my winxp client (whose name is Euro15), I see:

[2006/12/27 11:52:31, 2] smbd/sesssetup.c:setup_new_vc_session(799)
  setup_new_vc_session: New VC == 0, if NT4.x compatible we would close all
old
resources.
[2006/12/27 11:52:31, 0] auth/auth_util.c:create_builtin_administrators(785)
  create_builtin_administrators: Failed to create Administrators
[2006/12/27 11:52:31, 2] auth/auth_util.c:create_local_nt_token(899)
  create_local_nt_token: Failed to create BUILTIN\Administrators group!
[2006/12/27 11:52:31, 0] auth/auth_util.c:create_builtin_users(751)
  create_builtin_users: Failed to create Users
[2006/12/27 11:52:31, 2] auth/auth_util.c:create_local_nt_token(926)
  create_local_nt_token: Failed to create BUILTIN\Users group!
[2006/12/27 11:52:31, 2] smbd/reply.c:reply_tcon_and_X(711)
  Serving IPC$ as a Dfs root
[2006/12/27 11:52:37, 1] smbd/sesssetup.c:reply_spnego_kerberos(310)
  Username EURO/euro15$ is invalid on this system
[2006/12/27 11:52:37, 0] smbd/service.c:make_connection_snum(920)
  '/var/amavis/virusmails' does not exist or permission denied when
connecting t
o [spam] Error was Permission denied
[2006/12/27 11:52:37, 1] smbd/sesssetup.c:reply_spnego_kerberos(310)
  Username EURO/euro15$ is invalid on this system
[2006/12/27 11:52:37, 0] smbd/service.c:make_connection_snum(920)
  '/var/amavis/virusmails' does not exist or permission denied when
connecting t
o [spam] Error was Permission denied

Now, /var/amavis/virusmails exists, euro15$ is my XP client name, and I
don'd understand why samba uses this to get credentials. 
I mean I expect to see EURO/massimo (my username) in this line, not my
machine name.
This folder is owned by amavis, but massimo is in amavis group so it is ok
and I underline that this worked in the past.
What else could I do?
Thanks