Because everything seems to work fine in the Finder, the hardware and most
of the software is probably good. There are two more System resources that
are pulled in when printing in the background under MultiFinder:
Backgrounder and PrintMonitor. You may be experiencing a version
incompatibility between these files. This is likely if you've recently
upgraded your operating system.
We suggest replacing both of these files from a known-good 6.0.5 Printing
Tools diskette. You can drag-copy them, but make sure you've booted your
hard drive in Finder-only first. If you have a Spool folder in your System
folder, throw that away too.
If that fails, try trashing and reinstalling the complete operating system
using the Installer.