samba - Jun 2012 - Samba 3.6.3 on Ubuntu Server 12.04 Server Problem (Urgent)

I upgraded a machine that had been configured as a PDC running Ubuntu Server
11.04 (and whatever version of Samba was default in July 2011) to the new Ubuntu
12.04 Server LTS, which has Samba 3.6.3 (I did a fresh install).  I restored the
existing samba configuration file (smb.conf), and re-created the user accounts
(both adduser and smbpasswd).  The PDC serves roaming profiles to user on
Windows 7 Professional and Windows XP Professional computers.

I then removed each computer from the domain (changed to workgroup
"WORKGROUP") and then re-added three computers to the domain.  Each
initially worked, connecting to the domain, and downloading the user's
roaming profile.  I was able to logon and logoff successfully a few times, then
started getting the following error: "There are currently no logon servers
available to service the logon request.".

When that error appeared the first time, I was able to reboot the client (Win7)
machine, and then logon to the domain successfully once, and then the error
message would reappear at the next attempt to logon (a few minutes later).  This
worked two or three times, and has since failed - I get the same error message
no matter what now.

I am still able to ping and SSH into the PDC, so connectivity is still there,
just not when I try to use it as a PDC!

Does anyone know if there is anything in Samba 3.6.3 that has changed that would
cause this strange behavior?

(Attached is my smb.conf file & the samba log from one of the affected
machines.)

Thanks in advance for any help that you can provide!  I have to have this server
back up and running by Monday morning, even if it means rolling back and
re-installing Ubuntu Server 11.04.
Greg
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: smb.conf.txt
URL:
<http://lists.samba.org/pipermail/samba/attachments/20120617/527a96b9/attachment.txt>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: log.lpfrontdesk-2.txt
URL:
<http://lists.samba.org/pipermail/samba/attachments/20120617/527a96b9/attachment-0001.txt>