You modify the data channel port range and configure your firewall to allow the traffic in the port range.
When you try to use FTP over SSL you get "could not retrieve directory listing" error message.
One of the reasons for this is that the data channel port range changes does not take affect until you restart the Microsoft FTP Service.
You need to restart the Microsoft FTP Service for the changes in the data channel port range to take affect. Restarting the IIS services (e.g.: using IISRESET command, which is not recommended) is not enough.