Resetting the server isn't an option. We've got 40+ websites on our Managed Wordpress account.
The SFTP credentials specify port 22. That's what I've been using and as I mentioned, it sometimes works, albeit very rarely. In any case, I tried port 21 and I got the same error.
I tried using FileZilla instead of Transmit and that worked. However, when I first connected I got a warning:
The server’s host key is unknown. You have no guarantee that the server is the computer you think it is.
It prompted me to save the SHA key in the FileZilla cache, which I did. I then disconnected and tried to connect again. This time I got:
Warning Potential Security Breach! The server’s key does not match the key has been cached.
I'll admit I'm not too familiar with how server keys work. What is going on? I shouldn't need to use a separate FTP app for this one single site. All the other sites seem to work fine. What is different about this one?