If you use WinSCP to transfer backups with the user backuser to manually copy backups from or to TightGate-Pro, advanced settings must be made in WinSCP, otherwise the login will fail or the connection will be terminated immediately:
Create a new connection definition in WinSCP. There as protocol SCP as the protocol.
Under the menu item Advanced > SCP/Shell in the menu item Shell enter the following: /bin/loginbash
Under the menu item Advanced > Directory > Remote directory enter the following: /home/backuser/backup
Save and connect.