FTP errors on shared or Linux servers

I've been using Opus for (S)FTP for ages now without issue, connecting to Windows VPS's or cloud servers of one type or another.

Recently I've been having issues though when trying to connect to either a Windows domain on a shared server (3rd party hosting) when it fails with:
501 Syntax error in parameters or arguments.

and also trying to connect to a Linux (Ubuntu) VPS where it fails with:
SSH: Fatal: Received unexpected end-of-file from SFTP server

In both cases these errors occur after successfully connecting and logging in - but it can't get any further than that, and closes the connection after displaying these errors in the logs.

Any ideas? Thanks.

Meh - must have been something at the server end. Having got in touch with their tech support they've done something (I know not what) and it all works OK now.