88471.852 Error MainLoop.cpp:1207: Exception at tick 11484212: The mod RailPowerSystem (0.4.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RailPowerSystem::on_pre_player_mined_item (ID 11)
RailPowerSystem/methods/globalEvents.lua:64: attempt to index field '?' (a nil value)
stack traceback:
RailPowerSystem/methods/globalEvents.lua:64: in function 'OnRemoved'
HermiosLibs/controlLib.lua:92: in function <HermiosLibs/controlLib.lua:86>

I go this exact error right now. But i was removing a powered rail not a vanilla one.
Update: Using drones to remove rails seems to not crash, only when removing by hand does it happen.
Update2: Seems to be related to https://mods.factorio.com/mod/RailPowerSystem/discussion/5e90d062b03149000cf00508
If rail is placed by one of these drones the powerlines aren't set down when the track is set down. When removing those tracksby hand it crashes because the power lines don't exist. ALSO when removing powered tracks with powerlines with said drones the powerlines don't get removed. Seems like some events are being missed causing these updates not to happen. There seems to be no way to remove orphaned powerlines....

Hi guys,
Thanks for the feedback. I definitely need to update the mod, it is old and not accurate anymore. Unfortunately, no time yet for this. I do my best to do it.
Just be patient :)
Thanks
Niko

http://bladeinc.be/downloads/Factorio/RailPowerSystem_0.4.2.zip

This fixes the crash for both rails and waterways.
i do not have a fix for the powerlines sadly.

Waiting for Hermios to update his mod too so it can be used without issues :) At least it is working without crashing for now.