If you create an entry, you'll need to make sure the spool directory exists and has the correct permissions. You want the printer daemon, which is usually run as user lp, to have access to the spool directory. You'll have to run these commands as root:

# mkdir -p /var/spool/lpd/lp
# chown lp /var/spool/lpd/lp
# chmod 700 /var/spool/lpd/lp
# checkpc -f
# /etc/init.d/lprng restart

LPRng includes a helpful tool for checking your printcap. It will even set up the spool directory for you, if you forget to do it manually:

# checkpc -f

Finally, restart the lpd. You'll need to do this any time you change the printcap, in order for your changes to take effect. You may need to use lpd instead of lprng:

# /etc/init.d/lprng restart

The older Berkeley printing system doesn't include a checkpc tool, so you'll have to try printing pages to your various printers yourself to make sure the printcap and spool directories are correct.