One of our players had the below error when opening the GUI

https://i.imgur.com/xPLRrbV.png

Can you provide more information, like how I can reproduce the bug?
Also, are there any enemies mods used?
Did it happen in single player or MP game?
If in MP game, did it happen to just one player or other players as well?

quote from the player was .. "I'm not sure what caused the error, it was after the server was restarted. I logged in and that error came up immediately."

JD's multiplayer server is using many biter mods. List of all the mods are below

ArmouredBiters_1.0.1
artillery-bombardment-remote_0.18.0
AtomicArtillery_0.2.0
billbo99_spawn_tweaks_1.1.1
biter_extermination_18.0.1
biter_hunt_group_18.0.5
biter_reincarnation_18.0.10
bullet-trails_0.5.1
Clockwork_0.18.5
Construction_Drones_0.6.11
DeathMarkers_0.3.1
Death_Counter_0.0.3
DoingThingsByHand_0.1.0
Explosive Excavation_1.1.7
extra_biter_control_18.1.5
flib_0.4.1
FX-by-Streamers_1.0.1
hardened_pipes_1.0.0
inbuilt_lighting_18.1.9
jd_plays_18.1.2
landmine-thrower_18.0.1
muppet_gui_18.0.2
muppet_streamer_18.0.5
Natural_Evolution_Enemies_0.18.05
Rampant_0.18.17
RateCalculator_1.1.4
SchallAlienLoot_1.0.1
SchallAlienMutation_0.18.2
SchallAlienTech_1.0.1
SchallArachnidPlatoon_1.0.0
SchallArtillery_1.0.0
SchallEndgameEvolution_0.18.5
SchallLandMine_1.0.0
SchallPickupTower_1.0.0
SchallRemainsPickup_0.18.1
SchallTankPlatoon_1.0.1
Shield-FX_0.18.4
SolarWalls_0.0.12
sonaxaton-infinite-resources_0.4.4
TheDeadBurn_v17-0.18.2
ThingsGoBoom_0.0.3
train-pubsub_1.0.5
TSM-outpost-builder_0.0.7
TSM-outpost-builder_0.1.2
Turret-Shields_0.18.41
WhereIsMyBody_0.1.3

Guess it was caused by the button being clicked very soon after game load.
It should be solved (hopefully) by the additional checks in the latest release 0.18.6 / 1.0.0.
Thanks for reporting.