The error appears to be Samba complaining that the NT domain groups are not properly set up. You may need to create the group mappings. I've got script that I use on my Samba servers. You will want to change Linux GID's used in the script to suit your system.
Code:
#!/bin/bash
#
# initgroups
# Script to initialize the Samba groups to UNIX/Linix groups.
#
# Written by Charles Rutledge
# Copyright (c) 2005 Centauri Computer Works, Inc.
#
# This program is licensed under the terms of the GNU General Public License,
# Version 2 (or at your option, any later version) as published by the Free
# Software Foundation, Inc., 59 Temple Place, Suite 220, Boston MA 0211, and
# available online at http://www.gnu.org/copyleft/gpl.html.
#
# THIS PROGRAM IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER
# EXPRESSED OR IMPLIED. YOU ASSUME ALL RISKS FOR THE USE OF THIS PROGRAM.
#
# Map Windows NT Domain Groups to UNIX/Linux groups.
#
[ `grep -c ^smbadmin /etc/group` -eq 1 ] || groupadd -g 96 smbadmin
net groupmap modify ntgroup="Domain Admins" unixgroup=smbadmin comment="Designated administrators of the domain"
net groupmap modify ntgroup="Domain Users" unixgroup=users comment="All domain users"
net groupmap modify ntgroup="Domain Guests" unixgroup=nobody comment="All domain guests"
#
# Map Windows NT Domain Groups to UNIX/Linux groups.
#
[ `grep -c ^smbadmin /etc/group` -eq 1 ] || groupadd -g 96 smbadmin
net groupmap modify ntgroup="Domain Admins" unixgroup=smbadmin comment="Designated administrators of the domain"
net groupmap modify ntgroup="Domain Users" unixgroup=users comment="All domain users"
net groupmap modify ntgroup="Domain Guests" unixgroup=nobody comment="All domain guests"
#
# Create a Unix group for Windows machine accounts.
#
[ `grep -c ^machine /etc/group` -eq 1 ] || groupadd -g 500 machine
#
# Map Windows NT machine local groups to UNIX/Linux groups.
#
[ `grep -c ^ntadmin /etc/group` -eq 1 ] || groupadd -g 544 ntadmin
net groupmap modify ntgroup="Administrators" unixgroup=ntadmin comment="Members can fully administer the computer/domain"
[ `grep -c ^ntusers /etc/group` -eq 1 ] || groupadd -g 545 ntusers
net groupmap modify ntgroup="Users" unixgroup=ntusers comment="Ordinary users"
[ `grep -c ^ntguest /etc/group` -eq 1 ] || groupadd -g 546 ntguest
net groupmap modify ntgroup="Guests" unixgroup=ntguest comment="Users granted guest access to the computer/domain"
[ `grep -c ^ntpwrusr /etc/group` -eq 1 ] || groupadd -g 547 ntpwrusr
net groupmap modify ntgroup="Power Users" unixgroup=ntpwrusr comment="Users granted most administrative on local computers with some restrictions"
[ `grep -c ^ntacctop /etc/group` -eq 1 ] || groupadd -g 548 ntacctop
net groupmap modify ntgroup="Account Operators" unixgroup=ntacctop comment="Members can administer domain user and group accounts"
[ `grep -c ^ntsysop /etc/group` -eq 1 ] || groupadd -g 549 ntsysop
net groupmap modify ntgroup="System Operators" unixgroup=ntsysop comment="Members can administer domain servers"
[ `grep -c ^ntprtop /etc/group` -eq 1 ] || groupadd -g 550 ntprtop
net groupmap modify ntgroup="Print Operators" unixgroup=ntprtop comment="Members can administer domain printers"
[ `grep -c ^ntbackup /etc/group` -eq 1 ] || groupadd -g 551 ntbackup
net groupmap modify ntgroup="Backup Operators" unixgroup=ntbackup comment="Members can bypass file security to back up files"
[ `grep -c ^ntrepl /etc/group` -eq 1 ] || groupadd -g 552 ntrepl
net groupmap modify ntgroup="Replicators" unixgroup=ntrepl comment="Supports file replication in a domain"
[ `grep -c ^ntrdp /etc/group` -eq 1 ] || groupadd -g 553 ntrdp
net groupmap add unixgroup=ntrdp ntgroup="Remote Desktop Users" type=domain comment="Members can access computers remotely via the Remote Desktop"