lpstat -t   <--- prints a listing of the lp status
lpshut      <--- shuts down the lp scheduler

rm -fr /var/spool/lp/tmp
rm -fr /var/spool/lp/temp
rm -fr /var/spool/lp/fifos
rm -fr /var/spool/lp/requests

lpsched     <--- starts the lp scheduler and recreates rm'd directories
                 in /var/spool/lp

lpadmin -x by_printer  <---  remove the by_printer definition

lpsystem -t bsd cambridge  <--- defines a bsd <--> cambridge (print server)
                                link

lpadmin -p by_printer -s cambridge -T unknown -I any  <--- adds a printer 
                                                           definition back

accept by_printer
enable by_printer

The printer should work now!