I have a Xerox WC 7845 that gets stuck preprocessing every job. It will clear the top priority job after a reboot but then everything else gets stuck preprocessing. Have tried printing from Server and PC. Tried PCL6, PS, and Global Print Drivers.
Login as admin and try to perform an "On demand ovewrite" from Tools menu at the Security section.
And if this not solve your issue do a software upgrade or reinstall by AltBoot.