Suddenly, a few users get queue-based printers as "Not Available"

Suddenly, for no reason that is yet apparent to me, about a third of
the client PCs at a SBS 6.5.7 installation can't get jobs printed that
are put into print-queue printers. The jobs go in the queue and show
up in the queue, but never get printed. Other PCs on the same
server, same sub-net can put jobs into the same queue and it prints
for them.

This had all been working for all the PCs.

When I open up "Printers and Faxes" on the PCs that are normal, all
the printers say "Online". When I open up "Printers and Faxes" on the
PCs having print-issues, they show first as "Opening" and then as "Not
Available." All the other network-related stuff is normal - mapped
drives, etc.

When I look in with NWADMN32 the jobs say they are waiting on a
print-server.

I was all working fine last week. I'm not aware of making any changes
to the environment, unless it has something to do with a Microsoft
patch or a AV-update.

Warren