ExecuteCommand and call

I use WinSCP.dll with Visual Basic in VS 2008. FTPS (SSH).
Try execute commands like pwd, ls ... I use session.ExecuteCommand. I now that i can use session.ListDirectory ls is example.

when i try: session.ExecuteCommand("ls")

I have this Exception:
Error: WinSCP.SessionRemoteException: Server refused to start a shell/command ---> WinSCP.SessionRemoteException: Authentication log (see session log for details):
Using username "xxx".
Further authentication required

In log file i see when i try session.ListDirectory
Script: ls -- "/xxx//yyy/"
when i try session.ExecuteCommand("ls")
Script: call ls

I try Winscp.com connect to SFTP and run ls - this works. When i try "call ls" program ask for password and i have error: Further authentication required.

Why ExecuteCommand use call? What shoud i do to ExecuteCommand("ls") or ExecuteCommand("pwd")

First, please read below documents to better understand, what the Session.ExecuteCommand actually does. It may help you to realize that, what you are trying to do, may not make sense.
https://winscp.net/eng/docs/remote_command
https://winscp.net/eng/docs/shell_session
https://winscp.net/eng/docs/library_session_executecommand