Hi! I made it. It turns out to be a problem with our department network, not the LFS server. Thanks for the help!

Quote from Victor :

Strange.

One thing you can try :
-find the file cfg.txt which is located in your main LFS folder.
-open it
-replace "Master Port 29339" with "Master Port 8080"

Then try again.

It's not working :-(. What else can I do?

I think I got the correct password. When I try to start a new host in the demo mode, I got a same error. They look like this.

trying "ping lfs.net", I can indeed receive packages. However, I still cannot unlock the game. Same problem

I bought a S2 license. I tried to download the newest version and turned off the firewall, but I just can't unlock it. It keeps telling me "The program cannot connect to the server". I also have this result from the command window (See the picture). Is is a problem of the server, or me?