102681.906 Error MainLoop.cpp:1035: Exception at tick 7498503: Error while running event crafting_combinator::on_gui_click (ID 1)
Index out of bounds: 21
stack traceback:
...afting_combinator__/script/entities/RecipeCombinator.lua:103: in function 'update'
...afting_combinator__/script/entities/RecipeCombinator.lua:133: in function 'on_radiobutton_changed'
crafting_combinator/script/gui.lua:157: in function <crafting_combinator/script/gui.lua:133>
102681.909 Error ServerMultiplayerManager.cpp:96: MultiplayerManager failed: "Error while running event crafting_combinator::on_gui_click (ID 1)
Index out of bounds: 21
stack traceback:
...afting_combinator__/script/entities/RecipeCombinator.lua:103: in function 'update'
...afting_combinator__/script/entities/RecipeCombinator.lua:133: in function 'on_radiobutton_changed'
crafting_combinator/script/gui.lua:157: in function <crafting_combinator/script/gui.lua:133>"
102681.910 Info ServerMultiplayerManager.cpp:699: mapTick(7498503) changing state from(InGame) to(Failed)

I have zero clue as to what could be causing this error, or even how it could possibly be thrown in that particular location...

If I am to figure out what this is about, I'm going to need to know what you were doing when this happened, if this was a multiplayer game, and any other details.
From the error it seems you were doing something in multiplayer with the recipe combinator mode switches, but I tried switching them in all possible ways and it worked fine...

i was replacing a blast furnace mk1 to an mk2 in multiplayer