Access denied on new Directory Listing

We've been building a rather complicated web app. The Filebrowser module is just one of many features. In testing module we created several Directory Listings and they worked fine. This particular feature is supposed to be available to anonymous users. Suddenly, without changing versions of the module, new Directory Listings get an Acccess Denied for anonymous users. The permissions haven't changed. The old ones are still accessible to Anon users. The settings on the new Directory Listings are exactly the same as the ones on the old ones. I've done the typical thing of flushing cache, running update.php, etc. A bit flummoxed.