I have the same problem (version 5.7). But the problem arises always whenever I want to save the changed file on a remote server and that error message appears.
Can I make two future feature requests? It's sort of related.
On the FTP interface, can we have some way to indicate if it's SFTP or something? So far I know I can connect to SFTP by setting PASV connection on. But otherwise there's no way to tell.
Also can we have an option that if I leave the password field off in the FTP manager, it'll prompt me for a password everytime I use that connection? I'm paranoid and I don't trust myself. Hahah.
Non critical requests though. Maybe on v6.5 or v7 :)
Thanks again for the fix.