Thanks to Gerry Barton (and some luck on my part), I can offer a solution that worked for us when you get the "File not found or access denied" error message on a network. Essentially, our old desktop was not allowing shared sets and databases to "truly" be shared on our main machine (the one that holds the actual databases). To resolve this we created a new desktop (*.dtn) file while running in shared mode. We used a new name, and I can't recall if the other machine was up at the time (you may need to have just the machine giving you trouble up while you do this). But I can say the problem went away immediately.
Good luck to all!
John.