QTR-Quadtone RIP

Hi.... I've been printing fine all day with a 2400 in QTR 2.5.1 on a
Mac with OS 10.4.8.  Printed some prints in the morning, then some
step wedges in the afternoon.  Suddenly, however, I'm unable to print.
 Sometimes the printer will send the paper all the way through without
printing on it; sometimes nothing happens.  The Quad2400 status says
that it is "Waiting for device."  

I've tried removing and reinstalling the Quad2400 printer.  Restarting
both the printer and the computer.

The Epson driver does not work either.  

I've printed a nozzle check to verify that the printer is actually
working.

Any ideas?

Ed