NexentaStor unable to join Zentyal 3 domain

[faustotex]

What procedure should be followed to make NexentaStor 3.1.3.5 CE join a Samba4 domain controlled by a Zentyal 3.0.16 Domain Controller ?

I have unsuccessfully tried running Zentyal at domain levels 2003, 2008 and 2008 R2,where it now sits.
 
When I set lmauth_level=4 at the Nexenta side, I get the following errors after running "smbadm join -u Administrator mydomain.loc":

Apr  4 09:58:37 nexenta04 smbd[10056]: [ID 972153 daemon.error] smbns_ksetpwd: KPASSWD protocol exchange failed (Message stream modified)
Apr  4 09:58:37 nexenta04 smbd[10056]: [ID 702911 daemon.notice] Failed to set machine password.
Apr  4 09:58:37 nexenta04 smbd[10056]: [ID 871254 daemon.error] smbd: failed joining mydomain.loc (UNSUCCESSFUL)

If I set lmauth_level=2, the error then becomes:

Apr  4 15:43:32 nexenta04 smbd[10056]: [ID 807464 daemon.error] ndr_rpc_bind: smbrdr_ctx_new(S=dc02, D=mydomain.loc, U=Administrator), err=48
Apr  4 15:43:32 nexenta04 last message repeated 3 times
Apr  4 15:43:32 nexenta04 smbd[10056]: [ID 871254 daemon.error] smbd: failed joining mydomain.loc (LOGON_FAILURE)

What can be inferred from the above two sets of messages ?  Is there a problem with kpasswd or kerberos ?  What is a sensible way to debug this ?

This problem persists since Zentyal 3.0.3.

Note 1: The same NexentaStor installation joins a Windows Server 2003 domain without effort.

Note 2: The prior Solaris 11 11/11 joins the domain controlled by Zentyal also effortlessly BUT the more recent Solaris 11.1ga does not.

Help will be appreciated.