Error: attempt to index upvalue 'GeigerGUI' (a nil value). Help?

Hello. My first question.

So... I can't wrap my head around this...

local Player = game.Players.LocalPlayer
local GeigerGUI = Player.PlayerGui:FindFirstChild("GeigerCounter")

script.Parent.Equipped:Connect(function(Equip)
    GeigerGUI.Enabled = true
end)

script.Parent.Unequipped:Connect(function(UnEquip)
    GeigerGUI.Enabled = false
end)

Gives out the error:

23:36:05.477 - Players.rs1n1.Backpack.GeigerCounter.LocalScript:5: attempt to index upvalue 'GeigerGUI' (a nil value)

I have no idea why this happens.

This is in a local script. The GUI does exist.

LocalScripts can't detect if a tool is equipped? I remember using them for something like this not a long time ago.

Also, the files the things I'm messing with are in: https://imgur.com/a/WO3lv7L

https://imgur.com/a/a2oxEGa

Any ideas? Plz.