Sorry, I have absolutly no access to that server logs.

[Edit]
I grabbed that infos from a successfull cx, seems to be some java stuff, stucked at sftp version 3 :
Session protocol = SSH-2
SSH implementation = Maverick_SSHD
Encryption algorithm = aes
Compression = No
File transfer protocol = SFTP-3
------------------------------------------------------------
------------------------------------------------------------
Can change permissions = Yes
Can change owner/group = Yes
Can execute arbitrary command = No
Can create symlink/hardlink = Yes/No
Can lookup user groups = No
Can duplicate remote files = No
Can check available space = No
Can calculate file checksum = No
Native text (ASCII) mode transfers = No
------------------------------------------------------------
Additional information
The server does not support any SFTP extension.

Ok, your server disconnects, without any explanation, just after it receives the INIT message indicating that WinSCP supports SFTP v5. Do you have an access to server's log? Is there anything interesting indicating why it disconnects?

Here it is.

I have documented this:
https://winscp.net/eng/docs/rawsettings

Also i would be interested in the problem you are having with SFTP version 5.
Can you please attach or email me a complete session log file using login with SFTP 5?

WinSCP fails to connect to an SFTP server using version 5 of SFTP protocol.
From the UI, I'm able to downgrade to version 4, and then, the connection succesds.

How can I do the same thing with the COM interface ?


Thanks.

[EDIT]
I guess I found the trick.
SessionOptions.AddRawSettings "SFTPMaxVersion", "4"

[EDIT]
The trick works.
Notice that you can't change a previously set raw setting, you need a new SessionOptions object.