What I've seen is on Win 2000 client machines, all printers going through the SME 5.6 server say, under status: "Access denied, unable to connect".
I've set up a "50printers" template snippet to change smb.conf so that "guest ok = yes" in case there is a permission problem.
Didn't see this under <5.6. Curious part of this is:
1. Doesn't happen with Win9x clients;
2. On Win2K clients, you can still print, despite the message
3. If the job succeeds, the Win queue goes away; if the job does not succeed, you can't get into it to cancel the job.
Have seen identical symptoms on two networrks, so I assume this isn't spurious. I post this because it is similar, and may be related to your problem.
Tom