I also had the "general error" issue, even after following all the procedures listed in this thread.
I checked and re-checked all the settings, was able to make new registers in the lobby with success, but no conection after, allways the general error message.
My settings were:
LOCAL_IP_LOBBY.txt:
gtl-lobby.bierbuden.de
in the windows hosts file:
87.106.79.180 www.gtl-server.net
These values were the same that were shown in the Altbierbude updater, in the Configuration/Options/Lobby section.
here's how I fixed the issue:
I noticed that in my plr file, under multiplayer options, I had the following line:
Host IP Address="81.3.59.61"
(this was the backup lobby IP)
I changed this line to:
Host IP Address="87.106. 79.180"
(the same IP as in the hosts file)
Tryed to conect again, and still general error.
I registered in lobby again with a new name/password, and I could log in to multiplayer immediatly!
So, my advice is:
1 - Correct the line in plr/multiplayer options
2 - register in lobby again with new name/password
3 - try to log-in, but don't forget to use the name /password you used in step 2!