Network printers spit out garbage

Some of my network printers will suddenly for no apparent reason begin to print page after page of wingding like garbage. It can go on for several hundred pages if you let it run its course. Unpluging the printer for a few minutes clears it up. It then might be ok for a few days or even as long as a week, then it will happen again. At first I suspected the BUGBEAR virus, but scans of all servers and desktops have turned up no virus infections of any kind. Anyone out there have any ideas?

Thanks,
Mike Winstead