PureFTPd is the FTP server we use. It doesn’t say anything about the client being used.
It seems like you can connect to the FTP server, but switching to a secure connection fails. This is usually the result of a network configuration error.
Here are some things you can try:
Connect over a VPN to bypass the network issue.
Contact your network administrator or ISP about this. Or, if you are the network administrator, check your router settings whether the FTP ALG is turned on or off and toggle it.
Disable encryption on the FTP connection. But that should be a last resort, sending all FTP data, including your account password, over an unsecured connection is a really bad idea.