Cannot connect to SFTP server: "Server unexpectedly closed network connection"

[David]

Duplicate of bug #3823 (​http://trac.filezilla-project.org/ticket/3823) but could not find solution there.

The problem only is with some SFTP servers (actually I only know one).

I can establish a good connection with other servers, and can establish a good connection with both PuTTY (SSH) and PSFTP.

Messages:

Status: Connecting to server.example.org...
Trace: Going to execute "C:\Program Files (x86)\FileZilla FTP Client\fzsftp.exe"
Response: fzSftp started
Trace: CSftpControlSocket::ConnectParseResponse(fzSftp started)
Trace: CSftpControlSocket::SendNextCommand()
Trace: CSftpControlSocket::ConnectSend()
Command: open "user@…" 22
Trace: Looking up host "server.example.org"
Trace: Connecting to 1.2.3.4 port 22
Trace: Server unexpectedly closed network connection
Error: Server unexpectedly closed network connection
Trace: CControlSocket::DoClose(64)
Trace: CSftpControlSocket::ResetOperation(66)
Trace: CControlSocket::ResetOperation(66)
Error: Could not connect to server
Trace: CFileZillaEnginePrivate::ResetOperation(66)
Status: Waiting to retry...

[David]

Ooh, I forgot to add that (for this server) the problem is repeatable across multiple users/computers (I let 2 others try it)

[David]

I can confirm the issue is not present in the Linux version of Filezilla (Ubuntu 10.04, 3.3.1-1ubuntu1)

[David]

This problem still persists after an upgrade from Debian 4.0/etch to Debian 5.0/Lenny.
It is persistent across every (Filezilla) windows client I've tried on multiple computers and internet connections. WebDrive and WinSCP connect fine.