[Samba] Disapearing print share

[N. Yaakov Ziskind]

Samba 3.4.7 on Ubuntu Lucid; every so often, a workstation cannot print.
Restarting Samba fixes it. I finally noticed that, when broken, the
print share no longer shows up in 'smbclient -L'. And, I get messages in
the logs like:

[2010/07/30 12:16:11,  0] smbd/service.c:1202(make_connection)
  10.1.1.3 (10.1.1.3) couldn't find service petunia
[2010/07/30 12:30:26,  0] param/loadparm.c:8569(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/petunia
failed. No such file or directory

The next time that this happens, how do I begin to diagnose what's
really going on?

Thanks!