Simulation error Array index is out of range
Symptom
You will see this error on-screen - either while a saved game is loading, or in-game:
Simulation error: Array index is out of range.
There are several variants, each caused by a different mod or sometimes broken workshop asset. You can determine which one you have by searching for the above error message in your log file and then checking what is on the next line...
Cause / Solution
Array Index - Symptom 1
at WG_PopOnly.CommercialBuildingAIMod ...or something similar starting with
at WG_Symptom 1 has been fixed! Make sure you are using latest version of WG Configurable Population Modifiers mod.
Update November 2021: Use the Realistic Population Revisited mod instead.
Symptom 2
at PassengerTrainAI.SimulationStep ...or
at PassengerTrainAI.StartPathFind ...or something similar starting with
at PassengerTrainAIor
at MetroOverhaul.Detours.PassengerTrainAIDetour.StartPathFind
Symptom 3
at TransportLine.GetNextStop ...followed by
at BusAI.ArriveAtTarget ...
Symptom 4
at WaterSimulation.LockWaterSource ...at ImprovedPublicTransport2.Detour.VehicleManagerMod.ReleaseWaterSource ...
Symptom 5
at BuildingThemes.Detour.ZoneBlockDetour ...
Symptom 6
at BuildingAI.EnsureCitizenUnits ...
Symptom 7
at CargoInfoMod.CargoData.Count ...
Symptom 8
at UnlockManager.Unlocked ...
Symptom 9
Node is not connected to segmentWarning #: ExtSegmentEndManager.GetIndex(#, #): Node is not connected to segment.
Symptom 10
at TerrainModify.ApplyQuad ...at TerrainModify.UpdateAreaImplementation ...
Symptom 11
at TerrainManager.GetSurfaceCell ...Parameter name: indexfollowed byat System.Collections.Generic.List ...
Symptom 12
at GeneratedScrollPanel.IntializeUIAssetFilters
Symptom 13
at TransportLineAI.CheckNodePosition
Symptom 14
at EPTUI2.UITransportLineRow.Update
Array Index - Symptom 15
at TransportLine.GetNextStop#867: If the stack trace mentions aircraft or helicopters or blimps, it's likely due to building an airport/helipad/depot outside the central 25 tile area.
Array Index - Symptom 16
NetManager+Data.Deserialize#1195: Likely caused by outdated mods or broken road assets.
Use LSM "Safe Mode" (detailed further down this page) which can sometimes recover a broken save.
Use Compatibility Report mod which can help track down broken mods and suggest better alternatives.
General Solutions
There are some other things you can try...
Checking for broken mods and assets
Use Compatibility Report mod from Steam Workshop - it can help track down broken mods and suggest better alternatives.
Also, check the Steam Guide on Finding Broken and Bloated Workshop Subscriptions which can help track down other broken mods and assets.
Loading Screen Mod: Safe Mode
Some array index errors can be fixed using the "Safe Mode" options in Loading Screen Mod:
Exit game to desktop
Subscribe and enable Loading Screen Mod (LSM)
In its mod options:
Enable the optimization/sharing options to reduce RAM use (will make games load faster)
Enable the safe mode options
Now load your save - LSM will do everything it can to beat those errors
In some cases it might only work once, but the error will come back on the next load. If that happens, you'll have to try and track down what specifically is causing the error and fix it at source.
Was it Fixed?
Please post details of your error on the workshop page of the mod or asset causing the problem
You can often get help on the official Cities: Skylines Discord server.
If you use More Vehicles mod please note that lots of other mods aren't compatible as they generally hard-code the vehicle limit. The "Compatibility Report" mod will often tell you if that is the case.
TM:PE versions 10.21.1, 11.0 and later are all compatible with More Vehicles.
If you think it's caused by TM:PE, please Report a Bug (TM:PE users only, please - we can't help debug other mods, sorry) and we'll investigate.
Other problems? See: 👉 Troubleshooting