Thanks for responding. I have tried a command line just in case, but this will not work because the site is using SSL, and you need an SSL ftp client. The reason I mentioned firewall settings, is that everything I have found about this problem, which seems very common in a Google search, is directed at firewall settings as the culprit. The user has full permissions on the directory, so I don't see that it can be a permissions issue.
I forgot to mention - it works fine when I am inside our Sonicwall firewall, but not from the outside.
And another update, it doesn't look like the issue is MS specific. I installed Filezilla ftp server, and the same thing happens. I can connect, but not get a listing.