samba - Aug 2012 - "Network name no longer available" and other problems on windows client

Hello,

I have a samba server with a public share containing large text files that
are used as databases by software running on windows clients (Windows XP
x64 sp2 for the most part). Recently, I made some changes to my pipeline: I
changed the hardware of the samba server, and I upgraded the OS from Ubuntu
10.04 to 12.04 (which meant also upgrading smbd from 3.4.7 to 3.6.3). In
the mean time, the version of the softwares using the share was also
upgraded.

After all those changes, on the surface, everything works: I can map the
share to a drive on the win clients, open the share, and read or write
files. The softwares using the share are also able to read and write to the
mapped share. But those softwares often crash, or worse, have one of their
subprocess go in an infinite loop and never exit. And this does not happen
if I put the large text files locally on the windows workstation, so the
problems seems to have something to do with samba. When the software
crashes, I can often see a "Network name no longer available" in their
error logs. When their subprocess goes AWOL, I don't see any error message.

Here is my smb.conf:

[global]
>    workgroup = PROTEOMIQUE
>    server string = %h server (Samba, Ubuntu)
>    wins support = yes
>    name resolve order = wins lmhosts host bcast
>    dns proxy = no
>    #name resolve order = lmhosts host bcast
> wins
>    local master = yes
>    preferred master = yes
>    domain master = yes
>    host msdfs = yes
>    interfaces = eth0 lo
>    bind interfaces only = yes
>    hosts allow = 192.168.128.10 192.168.128.11 192.168.128.12
> 192.168.128.13 [...]
>    log level = 3
>    log file = /var/log/samba/log.%m
>    syslog only = no
>    syslog = 0
>    max log size = 10000
>    panic action = /usr/share/samba/panic-action %d
>    encrypt passwords = true
>    passdb backend = tdbsam
>    obey pam restrictions = yes
>    unix password sync = yes
>    passwd program = /usr/bin/passwd %u
>    passwd chat = *Enter\snew\s*\spassword:* %n\n
> *Retype\snew\s*\spassword:* %n\n *password\supdated\\
> ssuccessfully* .
>    pam password change = yes
>    map to guest = bad user
>
>    ## FF : Disabling printing
> functionality:
>    load printers = no
>    printing = bsd
>    printcap name = /dev/null
>    disable spoolss = yes
>
> [Databases]
>    path = /pubseq
>    read only = no
>    guest ok = yes
>    msdfs root = yes
>
I have set samba to log level 3, and I have been searching around and
investigating this matter for the last few days. But I have little
experience with network and samba administration and I'm way in over my
head with this and the many thousand lines of logs generated by the server.

Any help or any pointer as to how to diagnose and solve this problem would
be greatly appreciated!!!

Frederic