There are various potential reasons for encountering this issue, but it typically arises when the FTP LIST command fails due to an incorrect passive IP address or when the passive port range hasn't been forwarded from your router to the machine hosting Cerberus FTP Server.
If your network is equipped with a firewall or if your computer is situated behind a router, refer to the section on making your FTP server accessible from the Internet for detailed guidance.
For users with routers facilitating their computer's connection to the Internet via cable or DSL, it may be necessary to enable port forwarding. Consult your router's documentation for instructions on configuring port forwarding specifically for FTP.
As a recommendation, advise your clients to connect using passive FTP mode (initiated by the client with the PASV command). Unlike active FTP (initiated by the client using the PORT command), which necessitates configuring the client's network to permit incoming data connections, passive FTP is more universally compatible and is often preferred, especially for connections beyond local networks.