[Samba] Samba not responding from behind routers?

[Brian Coogan]

We have a weird problem with Samba 2.2.2-pre and 2.2.3a here and after
having gotten nowhere with all we'd tried I thought I'd ask the list.

Simply, Samba on problemserver doesn't respond to attempts to connect from
clients via our Cisco VPN concentrator.

     net use \\problemserver
gives
     System error 51 has occurred.
     The remote computer is not available.

We can ping, ftp and telnet host 139 to problemserver.  As we can reliably
connect to Windows servers (Windows 2000 and XP) from the same client, and
as we can't connect to any Samba servers, it does seem that the problem is
Samba specific.  As a side note, we can connect via our private dialup lines
to problemserver, just not via the Cisco VPN box.  This seems to suggest
that something is different when going through the Cisco box but for the
life of me I can't think what.

Telnet to port 139 on problemserver results in a whole lot of log messages,
but actual connect attempts never seem to produce any log messages even at
debuglevel 20, which does seem weird to me.

I'm not sure what else to try at this stage and would very much appreciate
hints and ideas!

Many thanks for all suggestions,

Brian