A quick update. No matter what I tried, I couldn't get the FTP site to connect to the UNC path, so I decided to change the site to a local path--got the same error. Out of frustration, I decided to just delete the FTP site and start over. This time I first set up the site with a local path, confirmed I could logon, then changed the path to the UNC path--everything is now working fine.
Maybe this was just some fluke, but things are working fine for the site now.
Thanks,
John