PDC not Validating SQL/Server connection - BDC Does

I have a WinNT 4 PDC abd BDC, both are at SP6a.

I have a Win2k member server, running SQL/Server 2000. Client PCs
running a VB6 application connect to the Win2k SQL/Server machine via
Named Pipes.

By pure chance today, while rebooting the BDC, I found I couldn't
connect to the SQL/Server machine from the VB6 application on the
client PCs. As soon as the BDC had finished booting, the client PCs
were able to connect.

When they couldn't connect, the client PCs received the error "SQL/
Server does not exist or access denied".

Doing a little more investigation, I found that if I start the
application from a client PC with the BDC on the network, it connects
fine as it has for years. If I then take the BDC off of the network,
by unplugging the BDC's network cable, that particular client still
connects. However, other clients that hadn't connected since the BDC
reboot, couldn't connect until I put the BDC back on the network.

During all of this, the PDC was always on the network, so it's obvious
that the PDC is unable to validate the connection of a client PC, but
the BDC can.

What would not be on the PDC that would keep it from validating the
client PC connection? Or is this a problem with the Win2k server, in
that it may only be looking for the BDC for access validation?

Thanks,

Joel