samba - Apr 2007 - new added users can't join from xp clients

Hello,
after upgrading a Debian samba server to 3.0.24 a few weeks ago,
everything seems to be ok until yesterday, when I've added a new user to
the domain. Now, the new user can join the shares from the samba server
from linux or win9x machines, but not from XP/2000 machines, wich
refuses to log in with ~ "User does not exits, or passwd is
incorrect..."

Old users can login ok from everywhere so this must to be related 
to new users added post upgrade.

The server is PDC for the domain, here's the smb.conf:
[global]
    workgroup = MONSSA
    netbios name = JOHANN
    server string = %h (Samba %v)
    passdb backend = tdbsam
    os level = 255
    preferred master = auto
    domain master = yes
    local master = yes
    security = user
    domain logons = yes
    logon path = \\johann\profiles\%U
    logon drive = z:
    logon script = login.bat
    encrypt passwords = true
    update encrypted = Yes
    unix password sync = yes
    passwd program = /usr/bin/passwd %u
    passwd chat = *Enter\snew\sUNIX\spassword:* %n\n
*Retype\snew\sUNIX\spassword:* %n\n *password\supdated\ssuccessfully* .

    add machine script = /usr/sbin/useradd -d /dev/null -g 300 -s /bin/false -c
"Cuenta de maquina" -M %u
    time server = Yes
    idmap uid = 10000-20000
    idmap gid = 10000-20000
    hosts allow = 192.168.1.
    guest account = nobody
    guest ok = yes
    map to guest = Bad User

Can somebody give a hint about this issue? I've reviewed three last months
of the list and found nothing similar to this.

Thanks a lot,
-- 
	Fernando M. Maresca
	Monitoring Station S.A.
	Calle 48 n? 812
	La Plata (B1900AHN) - BA - ARG
	Tel/Fax: (+54) 221 425 3355