Steps:

1] Create FARL train. I use 1-1-1.
2] Ghost out path in the front of the FARL train.
3] Add a curve next to you
4] Start FARL - you'll get a prompt to autodrive. Stay at this menu.
5] Drive sligtly on the curve and proceed in menu. You may need to try more than once.
6] Error message crashed game.

Vanilla Base + FARL:

Unexpected error:
221.221 Script control.lua:452: 9423 LuaEntity doesn't contain key target.
stack traceback:
[C]: in function 'create_entity'
FARL/FARL.lua:1572: in function 'deactivate'
FARL/FARL.lua:1505: in function 'activate'
FARL/GUI.lua:266: in function <FARL/GUI.lua:264>
(...tail calls...)
FARL/control.lua:366: in function <FARL/control.lua:360>
[C]: in function 'pcall'
FARL/control.lua:360: in function <FARL/control.lua:359>
224.738 Error MainLoop.cpp:788: Exception at tick 9634: Error while running event on_preplayer_mined_item (ID 11)
LuaEntity doesn't contain key target.
stack traceback:
[C]: in function 'create_entity'
FARL/FARL.lua:1572: in function 'deactivate'
FARL/control.lua:385: in function <FARL/control.lua:380>

3RA Mod Pack:

169.014 Script control.lua:451: 6117 LuaEntity doesn't contain key target.
stack traceback:
[C]: in function 'create_entity'
3Ra-AngelBobsPack/FARL/FARL.lua:1584: in function 'deactivate'
3Ra-AngelBobsPack/FARL/FARL.lua:1517: in function 'activate'
3Ra-AngelBobsPack/FARL/GUI.lua:278: in function <3Ra-AngelBobsPack/FARL/GUI.lua:276>
(...tail calls...)

http://i.imgur.com/2waEmjb.jpg

Keep in mind that my mod pack adds several lines to the start of lua files, which explains the difference in line numbers and shows that it seems to be the same error.

I have a hard time reproducing the error/crash. Managed it once, before putting any debugging into the code.. Next release will probably simply make it not crash until i find a way to properly fix it.