Hello Jaromir, 

  thanks for your reply and sorry for being so pushy before. 

> >   The server providing the share is a Windows 2k server; I can access
> > the share perfectly fine if using an interactive shell.  Running the
> > script (which is just some fancy options and directory modifications
> > before calling tar) by hand works, running it from cron doesn't. 
> 
> Would it be possible to try to cut the script into some minimal
> version which could be used to trigger the same problem?
> If the same problem happens when the script is run via 'at',
> you can use that to develop the minimal script.

I've been able to resolve the issue: I used to have the volume mounted
via /etc/fstab, the details being listed in /etc/nsmb.conf; that
always prompted the error.  I've now disabled this and am mounting and
unmounting the volume directly in that script, this leads to the
desired results. 

  Of course, I'm more than willing to do further investigations to
help in debugging; but for practical purposes, my immediate problem is
resolved. 

Thanks!
 Konrad