It definitely sounds like the issue is related to the server setup rather than your C# code or the WinSCP assembly itself.

SFTP and SCP may both run over SSH, but they work very differently under the hood. SFTP uses a dedicated subsystem on the SSH server, while SCP requires the server to allow execution of remote shell commands. The error:

“Server refused to start a shell/command”

usually means the SSH server either does not support SCP at all or is configured to block shell access/command execution.

Since your SolarWinds server works fine with SFTP but fails with SCP even in the regular WinSCP client, that strongly suggests the server only supports SFTP functionality. Many lightweight or test SFTP servers do not implement full SCP support.

A few things you could check:

* Verify whether the server explicitly supports SCP (not just SSH/SFTP)
* Make sure shell access is enabled for the account
* Test against another SSH server like OpenSSH to confirm your client code works with SCP
* Check whether the simulator environment is using a full SSH server implementation rather than a dedicated SFTP-only server

Your WinSCP assembly code is probably fine if simply changing:
`Protocol = Protocol.Scp`
causes the issue only on your local test server.

In short: SCP requires the server to execute remote commands, and your current test server likely does not allow that.

WinSCP needs a full shell access in the SCP mode:
https://winscp.net/eng/docs/requirements#scp
Your test server probably does not provide that.
But I'm confused about your requirements. You wrote that you were tasked with uploading to SFTP server. So was the original specification incorrect?
Anyway, if I understand it correctly and they are already using WinSCP (manually – GUI?) in the environment, where your code will run, then it must work, if you use the same session settings.
The GUI can generate the code for you:
https://winscp.net/eng/docs/ui_generateurl#code
You just might not be able to test it with your local test server.

Names of stations comes with codes such as ICTP00ITA, how do I find out the full name of the station

The SCP protocol is a very special thing. On its own, it supports file transfers only. But that's not enough for an application like WinSCP, which needs to be able to list files, and do other operations. So WinSCP is actually not a pure SCP client. It needs to use shell commands for some other operations. If your server support only pure SCP and not any *nix-like shell, WinSCP won't work. I do not know Solar Winds server, but most Windows "FTP" servers either do not support SCP at all, or do not support the features needed by WinSCP.
See https://winscp.net/eng/docs/requirements#scp and https://en.wikipedia.org/wiki/Secure_copy_protocol#Other_clients

Hi,
First, I'd like to say that this assembly is fantastic and very much appreciated. I was tasked with writing a small application that modifies weather product files (forecasts) and uploads them to an SFTP server. These files are then picked up by something called a continuous marine broadcast(CMB)/NAVTEX system and the file contents are sent to certain stations in a marine radio simulator. I went ahead and started writing the application after discovering the .NET WinSCP assembly. Everything went well. I installed a local SFTP server for testing (Solar Winds SFTP) and eventually had a working application doing exactly what I needed. I then found out that the workstations in the simulator (which are currently using WinSCP clients for transferring the files) are using SCP as the file protocol in WinSCP, not SFTP. Now I am not very well versed in the intricacies of SFTP/SCP/SSH but thought.. maybe I can just change the sessionOptions protocol to Protocol.Scp and set my solar winds SFTP server to SCP rather than SFTP and things may very well work in my development environment. Unfortunately, I am receiving exception "Server refused to start a shell/command." Even if I use the full blown WinSCP client I am receiving this error. In the simulator they are using a full blown WinSCP client also and are able to use SCP as the file protocol and put these files without issue. So would this issue have to do with my own Server setup? I have no issues at all when using Sftp as the protocol in my C# but I think I'll need to find a way to put these files using SCP if possible.

WinSCP log ends generally like this after exception:

Sorry if I rambled on, it's been a long day and this problem has had me all over the place. Any advice or help would be greatly appreciated.