Hello,
I've a rhel6 server on a vmware structure.
samba rpm are;
samba-common-3.5.10-115.el6_2.x86_64
samba-3.5.10-115.el6_2.x86_64
samba-winbind-clients-3.5.10-115.el6_2.x86_64

smb.conf
[global]
workgroup = AAAA
server string = TSTArchive
security = DOMAIN
passdb backend = tdbsam
log level = 3
local master = No
ldap ssl = no
cups options = raw
short preserve case = No
dos filetimes = Yes
dos filetime resolution = Yes
unix extensions = no
wide links = yes

# disable printing
load printers = no
cups options = raw
printcap name = /etc/printcap
show add printer wizard = no
disable spoolss = yes

Network:
IP=10.13.16.22 NETMASK="255.255.254.0"
GATEWAY="10.13.16.1" (it is on a different vlan in rspect to the dc)

I successfully join the domain:
> net join -w AAAA -S domaincontroller -U networkadmin

domaincontroller network:
IP= 10.13.0.49 NETMASK="255.255.252.0"
GATEWAY=10.13.0.3

and all is running fine for a while. After some time I'm not able to have the authentication to the DC:
> net rpc testjoin
Unable to find a suitable server for domain AAAA
Join to domain 'AAAA' is not valid: NT_STATUS_UNSUCCESSFUL

Some one can help me to fix it?
thank you in advance
romano

hello I found an answer,
since the samba server is located in a different subnet in respect to the domain controller the broadcat messages are blocked and the samba server could not authenticate any request for its resources.
The workaround consist to use the WINS service or lmhosts file, both to configure in smb.conf, I enabled lmhosts eg.
smb.conf:
workgroup = AAAA
server string = TESTArchive
security = DOMAIN
passdb backend = tdbsam
log level = 1
local master = No
ldap ssl = no
cups options = raw
case sensitive = yes
short preserve case = No
dos filetimes = Yes
dos filetime resolution = Yes
unix extensions = no
wide links = yes
name resolve order = lmhosts bcast wins hosts
encrypt passwords = yes

/etc/samba/lmhosts:
127.0.0.1 localhost
10.13.0.49 DomainController#20
10.13.0.49 AAAA#1b
10.13.0.49 AAAA#1c

bye
Romano