samba - Jul 2011 - Upgrade from 3.0 to 3.5 & preserve domain trust?

Hello,

We recently upgraded domain controllers to 2008 and were forced to
update "samba-3.0.33" to "samba3x-3.5.4". The upgrade path
was not just
update but rather erase samba and then install samba3x. Then I copied
the files under old config /etc/samba/* back to new install including
secrets.tdb.

Now, When I tried to validate the machine account using "net ads
testjoin", it prompted for HOSTNAME at REALM password which I didn't
know.
It should usually return "Join is OK".

Does anyone know, if we can retain the machine trust with Active
Directory and still upgrade samba? I have to upgrade another 20 machines
and do not want all machines to be joined and keytabs re-generated.

Thanks in advance