I believe the error message says it.

Why do you use SCP? Did you try SFTP?

I try to establish a WINSCP session to two different NOKIA Devices with SR-OS. I tried SFTP nad SCP. On the NOKIA devices I see the succesful login from WINSCP. After successful authentication the session stops working with an error regarding the start messege form the NOKIA SAS 7210" Fehler beim Überspringen der Startnachricht. Ihre Befehlszeile (Shell) ist möglicherweise nicht mit dieser Anwendung kompatibel (BASH wird empfohlen).
Following a part to the WINSCP log

. 2017-03-10 09:53:11.938 --------------------------------------------------------------------------
. 2017-03-10 09:53:11.938 WinSCP Version 5.9.4 (Build 7333) (OS 6.1.7601 Service Pack 1 - Windows 7 Enterprise)
. 2017-03-10 09:53:11.938 Configuration: HKCU\Software\Martin Prikryl\WinSCP 2\
. 2017-03-10 09:53:11.939 Log level: Normal
. 2017-03-10 09:53:11.939
. 2017-03-10 09:53:11.939 Working directory: C:\Program Files (x86)\WinSCP
. 2017-03-10 09:53:11.939 Process ID: 535356
. 2017-03-10 09:53:11.940 Command-line: "C:\Program Files (x86)\WinSCP\WinSCP.exe"
. 2017-03-10 09:53:11.940 Time zone: Current: GMT+1, Standard: GMT+1 (Mitteleuropäische Zeit), DST: GMT+2 (Mitteleuropäische Sommerzeit), DST Start: 26.03.2017, DST End: 29.10.2017
. 2017-03-10 09:53:11.940 Login time: Freitag, 10. März 2017 09:53:11
. 2017-03-10 09:53:11.940 --------------------------------------------------------------------------
. 2017-03-10 09:53:11.940 Session name: admin@192.168.88.21_SAS-MXP (Site)
. 2017-03-10 09:53:11.940 Host name: 192.168.88.21 (Port: 22)
. 2017-03-10 09:53:11.940 User name: admin (Password: No, Key file: No, Passphrase: No)
. 2017-03-10 09:53:11.941 Tunnel: No
. 2017-03-10 09:53:11.941 Transfer Protocol: SCP

2017-03-10 09:55:11.649 Access granted
. 2017-03-10 09:55:11.649 Opening session as main channel
. 2017-03-10 09:55:11.671 Opened main channel
. 2017-03-10 09:55:11.692 Started a shell/command
. 2017-03-10 09:55:11.741 Doing startup conversation with host.
. 2017-03-10 09:55:11.793 Skipping host startup message (if any).
> 2017-03-10 09:55:11.793 echo "WinSCP: this is end-of-file:0"
< 2017-03-10 09:55:11.813

< 2017-03-10 09:55:11.813

< 2017-03-10 09:55:12.168 *A:SAS-MXP# echo "WinSCP: this is end-of-file:0"

< 2017-03-10 09:55:12.168 WinSCP: this is end-of-file:0

. 2017-03-10 09:55:27.255 Waiting for data timed out, asking user what to do.
. 2017-03-10 09:55:27.255 Asking user:
. 2017-03-10 09:55:27.255 **Der entfernte Rechner kommuniziert seit 15 Sekunden nicht.
. 2017-03-10 09:55:27.255
. 2017-03-10 09:55:27.255 Weitere 15 Sekunden warten?** ()
. 2017-03-10 09:55:40.653 Attempt to close connection due to fatal exception:
* 2017-03-10 09:55:40.653 **Abgebrochen durch Benutzer.**
. 2017-03-10 09:55:40.653 Closing connection.
. 2017-03-10 09:55:40.653 Sending special code: 12
. 2017-03-10 09:55:40.654 Sent EOF message
* 2017-03-10 09:55:40.893 (EFatal) **Abgebrochen durch Benutzer.**
* 2017-03-10 09:55:40.893 Fehler beim Überspringen der Startnachricht. Ihre Befehlszeile (Shell) ist möglicherweise nicht mit dieser Anwendung kompatibel (BASH wird empfohlen).

Host startup message
TiMOS-B-8.0.R2 both/hops ALCATEL SAS-Mxp 22F2C 4SFP+ 7210 Copyright (c) 2000-2015 Alcatel-Lucent.
All rights reserved. All use subject to applicable license agreements.
Built on Fri Nov 6 13:42:05 IST 2015 by builder in /home/builder/8.0B1/R2/panos/main