Yep have the same error. Have tried it with 5 different users

You need to use the multiplayer patch engine.dll files posted in the sticky and start it as a dedicated server. You do that by setting all your settings in the host menu but instead of hitting start hit quit. Then go to the game folder and start swat4dedicatedserver.exe or swat4xdedicated etc if it's the expansion. To get people to join online you then give them your internet ip. You can find that by various sources such as what is my IP etc.

Bump, im having the exact same problem.

The Engine.dll for the new Master Server didn't help me much with direct IP connecting, but now I figured out what I did wrong all the time.

1. Forward the Ports 10480-10483 (maybe -10489)
2. Create LAN Server
3. Get external IP address on: http://whatismyipaddress.com/
4. Get your server Port from:
SWAT4_InstallDir\Content\System\swat4.ini
SWAT4_InstallDir\ContentExpansion\System\swat4x.ini
Default Port = 10480 or 10481
5. Your buddies can now join with the direct IP option in the Server Browser and APPEND the Port with : like this
12.345.67.89:10481

How do I get a new CD key from gog if mine is invalid

Hi, I'm having the same issue with the invalid CD key but where on earth do I enter the key? That's the biggest issue here for me, cuz if I actually knew where to enter the key then I could do it. The game installation didn't ask me for it because it was probably patched but then why would it ask me for the key then? I looked up some videos on youtube where they supposedly have cd keys you can try so that's what I'd like to do.

do you have find some solution? i have the same problem

Seems like their never gonna fix this...

I have the same problem, you don't know how to get the cd key

Please, for any "Invalid CD Key" issue, use the newer patch that I'm releasing here: https://www.gog.com/forum/swat_series/swat_4_multiplayer_patch/post1