I have an Epson Stylus Colour 680 USB inkjet printer.
Recently I started finding that I couldn't print sometimes in OS X - Print centre would just say "an internal error has occurred - try turning the printer off and on again" : classic apps would almost never print in OS X they'd complain about "a communications error" - but they would print flawlessly if booted into OS 9.
The problem ended-up being a new version of the OS 9 drivers - they *completely* bugger printing in X if classic is running at all. And classic printing always fails.
So If you have this printer DO NOT upgrade your classic printer drivers to version 6.4b (as available for download on the epson site.) It turns out that the old drivers (6.4a) are far more usable.