Hey. The TSS version of the patch was indeed crashing server. Could you try the updated version? https://github.com/sergeii/swat-patches/raw/master/swat4stats-masterserver/TSS/Engine.dll

The user (bporgn) came to my thread 2 days after posting the issue here.

I made a fix back in March.

https://www.gog.com/forum/swat_series/fixed_swat4x_server_hosting

If anyone visits this thread, you can find my solution above.

How to fix that the coop partner gets dropped from server each time the round ends?
Has to reconnect each time.

For example, both hit ready to start AGAIN, then it connects and loads, but i am alone in lobby soon after. While there is no other connection problem in a round. Only after a round / or at retry.

Sorry, this is a bit confused here or here are to many download links.
Could someone please explain to me what exactly I have to do to be able to play this game online or get the Gamespy in game Master server list up and running again?

Direct connect with ip works on itself.
If you want the other function, read the description. Its not much to do.

ok thank you very much!
I have meanwhile brought the server list up and running.

Now I just hope that there are reasonably friendly players on the way.
not like just now on the Server "MYT COOP SVR".

Сonnection to server has failed when trying to join ANY server, i`ve tried everything, what might cause the problem?

1º Error, CD KEY, SERIAL, NUMERO DE SERIE.
Cuando quieres iniciar un servidor/dedicado desde el menu del propio juego.
--Este error se genera, por que no estan los seriales, bien, puestos en la ruta del registro.
Equipo\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Sierra\CDKeys

-----------
Estos se pueden agregar creando un archivo *.reg
Archivo REG 64bit
Ejemplo del registro
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Sierra\CDKeys]
"swat4"=hex(3):67,9E,27,86,B9,83,10,77,AC,09,7C,6D,6B,5D,D6,70
"swat4xp1"=hex(3):B7,4B,8C,09,84,8C,9B,50,B4,B8,BA,93,C6,20,F6,CD
Ejemplo del registro
--*******Puede copiar el texto anterior, entre Ejemplo del registro y abrir el bloc de notas, pegarlo, guardarlo con un nombre y la extensión *.reg (luego puede ejecutarlo como administrador) y ya le dejara crear una partida desde el menu del juego.
--*******
NYD2-MAB8-REJ3-MYM6-4733
67 9E 27 86 B9 83 10 77 AC 09 7C 6D 6B 5D D6 70

XAX7-JEM3-FAT9-MYM9-7782
B7 4B 8C 09 84 8C 9B 50 B4 B8 BA 93 C6 20 F6 CD

¿Como puedo sacar mi archivo reg de mi KEY/SERIAL?
Use un CD de instalación dale e instalar, y cuando te pida el Serial, Escriba el tuyo.
Dale 1 vez a siguiente.
Ahora valla a la dirección del registro.
--64bit
[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Sierra\CDKeys]
--32bit
[HKEY_LOCAL_MACHINE\SOFTWARE\Sierra\CDKeys]

Haga clip derecho encima de ejm: swat4 y dale a exportar.

2º JUGAR ONLINE.

FIREWARLL WINDOWS.
El juego necesita que se agrege permiso en el FIREWALL de windows, de entrada y salida, para las aplicaciones:
Swat4.exe
Swat4DedicatedServer.exe
Swat4X.exe
Swat4XDedicatedServer.exe
PUERTOS ROUTER.
Necesario abrir los puertos en el router 10480,10481,10482,10483,10484,10485 TCP/UDP para crear un servidor dedicado.

Invalid CD KEY error has been fixed and added to patched DLL.

Check https://www.gog.com/forum/swat_series/swat_4_multiplayer_patch/post1