Cannot join PDC Nethserver domain

Dear all,
I just ended up deploying NethServer release 6.7 (final).
It acts also as DNS, DHCP disabled. It's configured as PDC for unionfidi.lan domain, IP address 10.0.0.200

[root@dc1 ~]# nslookup 10.0.0.200
Server:         127.0.0.1
Address:        127.0.0.1#53
200.0.0.10.in-addr.arpa name = dc1.unionfidi.lan.

I fired up a Windows 7 virtual machine, to test how it joins the domain, with PDC's IP address as DNS.
I get this message:

0x0000232D RCODE_REFUSED
An error occurred when DNS was queried for the service location (SRV) 
resource record used to locate an Active Directory Domain Controller (AD
 DC) for domain "unionfidi.lan".
The query was for the SRV record for _ldap._tcp.dc._msdcs.unionfidi.lan

Even not joined to domain, in computer network properties, domain suffix unionfidi.lan is present.
I performed an ipconfig/registerdns on Win 7, waited 15 minutes.
Then I did nslookup onto NethServer

[root@dc1 ~]# nslookup 10.0.1.249
Server:         127.0.0.1
Address:        127.0.0.1#53
** server can't find 249.1.0.10.in-addr.arpa: REFUSED

Drilling through logs, I found this entry:

winbindd/winbindd_dual.c:1342(child_handler) Could not write result

What am I missing to join the domain?
Thank you.