[Samba] Can't map ntgroup to unix group

[VSEC Saigon]

1. Here's my case:

[root at dsat ~]# net groupmap list
[root at dsat ~]# net groupmap add rid=512 ntgroup="Domain Admins" 
unixgroup=domainadmins
adding entry for group Domain Admins failed!

2. Here's samba log:

[root at dsat ~]# tail /var/log/smbd.log
[2006/10/10 08:51:23, 0] lib/smbldap.c:smbldap_connect_system(851)
  ldap_connect_system: Failed to retrieve password from secrets.tdb
[2006/10/10 08:51:23, 1] lib/smbldap.c:another_ldap_try(1051)
  Connection to LDAP server failed for the 15 try!
[2006/10/10 08:51:24, 0] passdb/secrets.c:fetch_ldap_pw(629)
  fetch_ldap_pw: neither ldap secret retrieved!
[2006/10/10 08:51:24, 0] lib/smbldap.c:smbldap_connect_system(851)
  ldap_connect_system: Failed to retrieve password from secrets.tdb
[2006/10/10 08:51:24, 0] passdb/pdb_ldap.c:ldapsam_search_one_group(2170)
  ldapsam_search_one_group: Problem during the LDAP search: LDAP error: 
(unknown) (Time limit exceeded)

Here's some setting in smb.conf

security = user
passdb backend = ldapsam:ldap://localhost
ldap admin dn = cn=admin
ldap suffix = dc=local,dc=atc
ldap user suffix = ou=People
ldap machine suffix = ou=Computers
ldap group suffix = ou=Groups