Early in the game, I was placing fast inserters (I'm not convinced that the placing caused this error, as I was placing a bunch of them) I was given an error message: "Error while running event Bottleneck::on_tick (ID 0) - invalid key to 'next'" and it exited the game.

This is in 0.16.25. After reloading the save and doing everything again, the error did not occur again. At the time of the error, the log file just shows what I put above, and that the error occured in MainLoop.cpp at line 1019, but I doubt that file is from Bottleneck.

This same error just popped up on me today while using the Upgrade Planner mod to replace 80 stone furnaces with 80 steel furnaces.

I reloaded the save, tried again, and again same crash.

Reload save, replaced 10 furnaces, no crash. Replaced 20 furnaces, no crash. Replaced 40 furnaces, no crash. I'm guessing there is an issue with the number of things being replaced in one go.

I have a save I can reliably reproduce this on. I am manually replacing Assembly Machine 1 with 2s.

When I replace each one, it will always crash after 3-4 assemblers are replaced.It seems to crash most reliably on the first 1-3 red assemblers.

https://www.twitch.tv/videos/247705752

I got this error too, in an on-going game, current version.

Just got it again.