Command not implemented with TLS/SSL connections

Hi all,
I am having a bit of an issue with connecting to a FTP server with Explicit encryption. The error comes back from the server saying Not Implemented. To make this even more puzzling this only happens on some computers, others will connect and work fine. I have exported the configuration from a working PC and imported on a non-working PC and this doesn't fix the issue.

I am using the most recent version of WinSCP, and some of the issues appear on brand new installs, others brand new installs will work out of the box without issue.

I have contacted the hosting company who have come back with the following:

This issue has popped up a few times recently, and we have done thorough testing to ensure that the issue isn't with our servers - and we found that the problem is client-side.

To be sure, I have just connected to your hosting service, using FileZilla on my end without issue.

What I can recommend doing is reinstalling WinSCP or consider using a different FTP client altogether.

We generally recommend using FileZilla for FTP.

The issue may also be related to your Windows 10 installation as there may have been an update that has caused these issues.

It is hard to say exactly what the cause is, however, I can certainly say that this isn't a server issue.

I would use FileZilla, however, I much prefer WinSCP, and FZ doesn't have the Keep remote directory up to date option.

Thanks in advance,
mrtechguy

This is all strange. The server reports itself as "Pure-FTPd", yet I didn't find the "Command not implemented for that parameter" error in Pure-FTPd source code. Nor did I find any reference for such error message for Pure-FTPd on the Internet.
For AUTH TLS command, Pure-FTPd returns either "234 AUTH TLS OK." or "500 Unknown command" (when TLS is disabled).

All references to "Command not implemented for that parameter" error message I have found are for FileZilla FTP server. But it never returns it for AUTH command either.

To me it looks like either a server-side bug in some non-standard/custom FTP server of your hosting company. Another options is that there's a firewall or a proxy between you and the server that intercepts the connection and (mis)translates it somehow.

Or that the server actually does not support an encryption. Are you aware that in the default configuration, FileZilla is actually trying an encryption, but if that fails, it automatically falls back to an unencrypted connection? Isn't that what is happening?

Can you post a log file of a successful connection with WinSCP from the other machines, where it works? And a verbose FileZilla log file from the machine, where WinSCP does not work? Also, can I have at least a hostname of your server? You can post it in a private attachment, if you do not want to post it publicly.

I certainly agree it is all a bit strange. I haven't yet tried FileZilla as a client on the non-working machines. The connections that are failing are always 4G connections, unfortunately I haven't been able to get the same failure but I will try your suggestions when I do.

I have attached (privately) an unedited log from a working machine, secure connections are definitely enabled and working (non secure connections are forbidden by the host).

I will try FileZilla next time I find a configuration where WinSCP throws the not implemented error.

Thanks!

OK, so once you have a chance, please collect WinSCP and FileZilla logs from the same machine in situation in which WinSCP fails and FileZilla works.