FTP is a funny protocol at the best of times (some say archaic), and getting it to work can be a pain in general not just with flexshares! Problems are often caused by incorrect firewall settings, DNS problems, or dodgy FTP clients. However saying that the flexshares go a long way to making creating an FTP Flexshare much easier
A browse over the ProFTPD docs will give you some idea as the complexity that you can put in place on an FTP server
I guess you have seen these docs?
That aside, it works just fine here...my biggest tip is NOT to use internet browsers to access FTP shares....they are very bad at following standards. Use a decent standalone FTP client like Filezilla for example, or even Windows Explorer
Can you elaborate a bit more on what is causing the problem?