I happened to figure this out when I put some of the referenced files on a proper web server, linked to them, and lauched the home page SWF from dropbox and it still did not work. Having isolated the problem at that point to dropbox, and remembering that unless I created a public link I am essentially working within a local files system, I tried dropbox's public link in the browser.
Champagne all around! Oh, darn, too early for that. More coffee instead.
JP