I had the same problem and could only figure out how to fix it by chmod 
777 /var/spool. chmod +s didn't work, either. I've read about this
problem
on other mailing lists.
> I must have a problem with ownership of the Samba directory that holds 
the > spooled file to be printed.  The only way that I can get a file to print 
on a > Unix shared printer from a Windows computer is to define the spool area 
R/W to > world, which is certainly not acceptable.  I've tried having root, lp, 
and > nobody as owners with no luck.  Also, I've tried "guest ok =
yes".  What
am I > missing?  Below is the [printers] definition from my smb.conf file on a 
Solaris > 7 computer.
> 
> Thanks, in advance, for your help.
> 
> Mike Box                       Phone: (540)231-9506
> Systems Administrator            Fax: (540)231-3863
> Department of Statistics      E-mail: Mike.Box@vt.edu
> Virginia Tech
> 
> 
> ---
> ...
> guest account = nobody
> printing = SYSV
> ...
> [printers]
>    comment = All Printers
>    path=/var/spool/lp/tmp/samba
>    print command=/usr/bin/dos2unix -ascii %s | /bin/lp -d %p -s | rm %s
>    browseable = no
>    printable = yes
>    public = yes
>    writable = no
>    create mode = 0700
> ;  guest ok = yes
> 
>