Debian client can't connect to Windows server

I’m trying to set up UrBackup for the first time.
Windows 10 is the server.
Debian Linux is the client.
Try to debug gets this:

urbackupclientbackend -i -v debug
2017-06-01 23:00:34: ERROR: urbackupserver: Failed binding socket to port 35623. Another instance of this application may already be active and bound to this port.
2017-06-01 23:00:34: FileSrv: Server started up successfully
2017-06-01 23:00:34: Started UrBackupClient Backend...
2017-06-01 23:00:35: Looking for old Sessions... 0 sessions
2017-06-01 23:00:36: Trying to connect to internet server "" at port 55415
2017-06-01 23:00:46: Connecting failed.

(IP address changed, but kept in same format)

Definitely able to access the web interface remotely from the external IP.
Server seems generally effectively configured as far as I can tell, client is configured automatically by a package downloaded straight from the server.

What should I look for to identify what went wrong?

EDIT: Problem 1 down:
Windows firewall was being dumb .

Now it’s saying: “Socket has error: 111”


Disable the firewall, then ensure internet connections are allowed, then RESTART THE URBACKUP SERVICE via task manager.
The last bit isn’t documented anywhere for some reason :confused: