[CentOS] CentOS 5: problem with samba as PDC

Hello all

i have successfully upgrade an old PDC samba server (debian woody) to a 
new centos 5.

Everything works fine except for one thing

1- i'm unable to add new computer to domain except with the root users. 
With others installations all users in the group "Domain Admins" was 
able, now i get tis error:

sh: /usr/sbin/useradd: Permission denied
[2007/12/18 17:33:26, 0] passdb/pdb_interface.c:pdb_default_create_user(329)
   _samr_create_user: Running the command `/usr/sbin/useradd -g computer 
-c "Workstation (genoveffo2$)" -M -s /bin/false "genoveffo2$"' gave 126

After a new group map "Domain Admins" -> root group the error is:

useradd: unable to lock password file
[2007/12/18 17:42:49, 0] passdb/pdb_interface.c:pdb_default_create_user(329)
   _samr_create_user: Running the command `/usr/sbin/useradd -g computer 
-c "Workstation (genoveffo2$)" -M -s /bin/false "genoveffo2$"' gave 1
useradd: unable to lock password file
[2007/12/18 17:47:10, 0] passdb/pdb_interface.c:pdb_default_create_user(329)
   _samr_create_user: Running the command `/usr/sbin/useradd -g computer 
-c "Workstation (genoveffo2$)" -M -s /bin/false "genoveffo2$"' gave 1

The right of the users in "Domain Admins" (alessice) are not sufficient.

This is my groupmap:

[root at pdc ~]# net groupmap list
System Operators (S-1-5-32-549) -> nobody
Replicators (S-1-5-32-552) -> nobody
Domain Users (S-1-5-21-2276015355-2619491448-3726653824-513) -> utenti
Guests (S-1-5-32-546) -> nobody
computer (S-1-5-21-2276015355-2619491448-3726653824-2117) -> computer
Power Users (S-1-5-32-547) -> nobody
Domain Admins (S-1-5-21-2276015355-2619491448-3726653824-512) -> root
Print Operators (S-1-5-32-550) -> nobody
Administrators (S-1-5-32-544) -> nobody
Domain Guests (S-1-5-21-2276015355-2619491448-3726653824-514) -> nobody
Contabilita (S-1-5-21-2276015355-2619491448-3726653824-2101) -> contabilita
Account Operators (S-1-5-32-548) -> nobody
Commerciale (S-1-5-21-2276015355-2619491448-3726653824-2099) -> commerciale
Backup Operators (S-1-5-32-551) -> nobody
Users (S-1-5-32-545) -> nobody

[root at pdc ~]# head /etc/group
root:x:0:root,alessice
[...]

from smb.conf:

add machine script = /usr/sbin/useradd -g computer -c "Workstation (%u)" 
-M -s /bin/false "%u"
	
What is wrong?
Thanks