I guess the problem probably lies in the config of cups or the ppd or the gimp^H^H^H^Hgutenprint modules for you printer.
Take a gander @ localhost:631 and plink around there. You might just find out you printer is "stopped".
Also, I recnetly had to fight with my Seiko-Epson-Ekowa RX600, usblp was borkified.
You might completely remove the config for the printer and redo it.