lprm removes jobs from the print queue on Linux
When the GUI applets don't work or have gone into hiding, you can use lprm to clear out the print queue
sudo lprm
will clear out all from the print queue of the default printer, There seems to be more options if you do
man lprm
Fortunately, system administrators and even individuals can remove job from the print queue using the "lprm" command.
Read more: Link - How to Remove Jobs From the Print Queue in Linux | eHow.com