The problem you describe is caused by a difference between the remote file services available to a logged in user (such as yourself) and those available to the host without anyone one logged in. In this particular case, when I we refer to "logged in," I we mean running a Finder desktop. Remote (and local) file systems accessed via the Finder are all mounted under /Volumes.
Qube! runs as a daemon, and so it doesn't access the Finder at all. In general, any file you access remotely from the Finder is going to be inaccessible to any Worker running on the farm unless you take steps to make sure the Worker has those file systems already mounted.
You should consult your OS X Mac administration documentation to learn more about how to mount your file servers either statically or dynamically so they are available to your Workers at render time. You will also want to set similar mounts on your client machines so that the paths to the files you access when you submit the job will be consistent with your Workers. Here's a link: http://www.bombich.com/mactips/automount.html