From the SE discord bug-report channel, apparently FARL "tries doing something with the space elevator internal rails." Here's my console dump

4.608 Checksum for script space-exploration-postprocess/control.lua: 25640445
4.749 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Fully Automated Rail Layer (4.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FARL::on_init()
FARL/control.lua:79: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
FARL/control.lua:79: in function 'getRailTypes'
FARL/control.lua:228: in function <FARL/control.lua:222>"
4.750 Info ServerMultiplayerManager.cpp:797: updateTick(4294967295) changing state from(CreatingGame) to(InitializationFailed)
4.750 Info CommandLineMultiplayer.cpp:216: Exit point.
4.753 Info ServerMultiplayerManager.cpp:141: Quitting multiplayer connection.
4.753 Info ServerMultiplayerManager.cpp:797: updateTick(4294967295) changing state from(InitializationFailed) to(Closed)
4.817 Info UDPSocket.cpp:218: Closing socket
4.819 Goodbye

possible related ?

Error while running event FARL::on_configuration_changed
FARL/control.lua:79: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
FARL/control.lua:79: in function 'getRailTypes'
FARL/control.lua:370: in function <FARL/control.lua:247>

See for more: https://pastebin.com/sps9KFe5

Getting the same as Hadelfix

The mod Fully Automated Rail Layer (4.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FARL::on_init()
FARL/control.lua:79: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
FARL/control.lua:79: in function 'getRailTypes'
FARL/control.lua:228: in function <FARL/control.lua:222>

Same issue affects me :(

I filed an issue: https://github.com/Choumiko/FARL/issues/111

The likelihood that the bug will be fix by the mod author is quite slim. the last commit th the repo was 2 years ago.

However the fix is luckily simple.

1. Open the FARL_4.1.2.zip in your mods directory

2. find the control.lua file and edit row 78:
   from:
   if proto.type == "curved-rail" then
   to:
   if proto.type == "curved-rail" and proto.items_to_place_this then

3. save the file and zip it all back to the mod directory.

4. PROFIT!

There is now a pull request with a fix: https://github.com/Choumiko/FARL/pull/112
I would not hold ny breath that it ever getting merged though...