Problem

When connecting to a remote site via FTP, going through SecureRelay, where the remote site is configured using the hostname, the following error appears in the log:

and the connection fails.

Resolution

This issue is due to the fact that Gateway needs to know whether the hostname resolves to an IPv4 or IPv6 IP address, to know what kind of commands to use to establish the data connection (PORT/PASV or EPRT/EPSV). Where Gateway is unable to resolve the hostname, this error occurs.

A fix for this issue is being pursued. For now, the workaround would be to use the IP address (which you've already found works), or to create an entry in /etc/hosts on Gateway that maps the hostname to the IP (v4 or v6) address.