Die Mod RoboTank hat einen nichtbehebbaren Fehler verursacht.
Bitte informiere den Modautor über diesen Fehler.

Error while running event RoboTank::on_tick (ID 0)
RoboTank/control.lua:180: attempt to index field 'last_user' (a nil value)
stack traceback:
RoboTank/control.lua:180: in function 'player_index_of_entity'
RoboTank/control.lua:358: in function 'find_entity_controller'
RoboTank/control.lua:518: in function 'find_or_create_entity_controller'
RoboTank/control.lua:535: in function 'found_an_entity'
RoboTank/control.lua:557: in function 'find_unassociated_entities'
RoboTank/control.lua:1526: in function <RoboTank/control.lua:1515>

What version of Factorio are you running?

What other mods are you using, and what version of each?

Would you describe what you were doing in game at the time of the crash? Also, were you playing single-player or multiplayer?

I use the lastest Version for Factorio and Mods. I use many Mods (around 40 - mostly to increase the gameplay harder, QoL and so on). I will later give you a full list of my mods.
The Bug occured after putting this mod to an existing Session. I have 5 extra heavy Tanks (Schallfalkes Mods Tank Platoon, Gun Pod and so on) fully equipped with laser defence, minigun defence, reactors and so on. Then clicked on the tanks and Error massage.

Now it just is enough to put the Mod as active and load a save file that this Error message occures:
Die Mod RoboTank hat einen nichtbehebbaren Fehler verursacht.
Bitte informiere den Modautor über diesen Fehler.

Error while running event RoboTank::on_tick (ID 0)
RoboTank/control.lua:180: attempt to index field 'last_user' (a nil value)
stack traceback:
RoboTank/control.lua:180: in function 'player_index_of_entity'
RoboTank/control.lua:358: in function 'find_entity_controller'
RoboTank/control.lua:518: in function 'find_or_create_entity_controller'
RoboTank/control.lua:535: in function 'found_an_entity'
RoboTank/control.lua:557: in function 'find_unassociated_entities'
RoboTank/control.lua:1526: in function <RoboTank/control.lua:1515>

My Modlist taken from Mod-List.json.

AAI-CraftTab
aai-programmable-vehicles
aai-signals
aai-vehicles-hauler
aai-vehicles-miner
aai-zones
AdjustableSciences
Advanced_Machines
alien-biomes
alien-biomes-hr-terrain
alien-module
AllFurnaceswithModules
Bio_Industries
bobassembly
bobinserters
boblibrary
boblocale
bobmining
Bottleneck
cncs_Sulfur_Mod
Compound_Splitters_Continued
deadlock-beltboxes-loaders
Electric Furnaces
ElectricTrain
Factorissimo2
FARL
fish_slurry
Geothermal
LootMilitaryScience
Nightfall
Noxys_Waterfill
OmegaDrill
OpteraLib
Power Armor MK3
Power_To_Liquid_updated
quarry
ReStack
reverse-factory
robotworld
Robot_Battery_Research
robot_tree_farm
scattergun_turret
SchallAlienLoot
SchallAlienMutation
SchallAlienTech
SchallAmmoTurrets
SchallBeltConfiguration
SchallEndgameEvolution
SchallGunPod
SchallLampContrast
SchallRechargingWeapon
SchallRemainsPickup
SchallTankPlatoon
Single-Splitter-new
SolarWalls
sonaxaton-infinite-resources
stdlib
StorageTank2
Swarmageddon
Texugo_windgenerator
Turret-Shields
VehicleGrid
VersepellesAquaFarm015
Warehousing
WeakEnemies
Wood_Gasification

I played with SchallTankPlatoon and RoboTank for a while but could not reproduce the problem. I suspect it is related to one of the other mods. If you're willing to upload your saved game somewhere I can possibly use that to reproduce the issue.

In any case, I attempted a blind fix based on the stack trace you posted. Please try RoboTank 1.0.1, just released, and let me know whether it works.

However, be aware that making a RoboTank requires a vanilla tank as an ingredient, and SchallTankPlatoon disables the recipe for vanilla tank by default. You have to make a change to its configuration (in the GUI) to re-enable the vanilla tank recipe. Furthermore, although any of the modded vehicles can function as a commander, the RoboTanks themselves are just copies of the vanilla tank. You won't be able to let the AI drive any of the modded vehicles. If there is strong interest in that feature I might try to add it, but it will be a significant effort.

Hi smcpeak,
I am the author of Schall Tank Platoon. I have added some text in my description and FAQ, for instructing players who use both our mods, to keep the recipe of vanilla tank. Hope this will help.
Regards,
Schall

Great, thanks! I've added a link in RoboTank's description to your FAQ.