usb printer hangs until reboot

[michael <linux@networkingnewsletter.org.uk>]

Earlier today I could not use my USB printer. Looking at `ps -elf|grep
usb` it continuously had process state 'D' ("uninterruptible sleep
(usually IO)" according to `man ps`) and the CUPS web interface
continually reported "usb printer busy" (or something very similar). I
couldn't work out how to sort this out so resorted to a reboot and now
it all works fine.

My questions are thus:
- any ideas what might have happened? or where to look for clues (I
couldn't find anything in the /var/log files I checked)
- any ideas on how to resolve it without rebooting if it happens again?

I've done a Google but to no avail

Thanks
-- 
Michael Bane
Atmospheric Physics Group
University of Manchester