Hmm.
apollo:/usr/src/sys/vfs/hammer> ls -la /usr/bin/lpr
-r-sr-sr-x 1 root daemon 26588 Oct 21 21:46 /usr/bin/lpr
Make sure lpr is suid & sgid root:daemon. I am assuming your
filesystems aren't being mounted with the nosuid or nosgid mount
flags as well.
If lpr can't access the socket it kinda sounds like it isn't running
sgid.
-Matt