[Samba] after joining the domain the server loose the domain controller

[deep ramcrazy]

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

I've a dubt that with different vlan the DC and the samba server cannot communicate, but I'm not sure and in which way bypass it.
Thank you
Kind Regards
Romano