For details about error message "Cannot initialize SFTP protocol. Is the host running a SFTP server?" see:
https://winscp.net/eng/docs/message_cannot_initialize_sftp_protocol

Jazzykeith wrote:

I have Ubuntu Linux running on an Amazon "small" instance server. It has been working ok until now
When logging in I get the message "
---------------------------
Cannot initialize SFTP protocol. Is the host running a SFTP server?
---------------------------
OK Reconnect (1 s) Help
---------------------------

This was working ok and no changes to winscp have been made . We can connect via putty with no error. To the best of my knowledge nothing has changed on the Amazon server

Can you post a log file both from WinSCP and PuTTY?

I have Ubuntu Linux running on an Amazon "small" instance server. It has been working ok until now
When logging in I get the message "
---------------------------
Cannot initialize SFTP protocol. Is the host running a SFTP server?
---------------------------
OK Reconnect (1 s) Help
---------------------------

This was working ok and no changes to winscp have been made . We can connect via putty with no error. To the best of my knowledge nothing has changed on the Amazon server

I had this issue and it turned out to be because I had added a new script to my .cshrc (the csh equivalent to .bashrc) that required a tty in order to run. When WinSCP tunnels over ssh there isn't a tty, so it couldn't run the script and couldn't log in.

I had an error in my .bashrc login script and this was causing the error

Please read documentation for common reasons of getting this error and some resolution hints.

Turns out my password on the server had expired. I reset my password and am able to connect fine.

I am using version 4.0.4 (build 346) with explorer like environment.

The protocol is setup as SFTP Yes, Allow SCP Fallback.

When I try to logon to the server, I get the following error:
"Connection has been unexpectedly closed. Server sent command exit status 1. Cannot initialize SFTP protocol. Is the host running a SFTP server?"

My colleague has the same configuration but is running version 3.8.2 and is able to connect.

What could be the problem?

Thank you.