Custom Disaster script?

Try doing this, put this code in a LocalScript instead, and use this revised code. Your problem is PlayerGui is not apart of players, but is apart of the Player that is in Players

Tell me if it works or not

local A = "event1"
local Lighting = game.Lighting
local Choos = 0
local Players = game.Players.LocalPlayer

while true do
    Choos = math.random(8)
    wait(4)
    if Choos == 2 then
        a = script:findFirstChild("GuiA"):Clone()
        a.Parent = Players.PlayerGui
        wait (5)
        a = Players.PlayerGui:findFirstChild("GuiA"):Destroy()
        b = script:findFirstChild("GuiAA"):Clone()
        b.Parent = Players.PlayerGui
        game.Lighting:findFirstChild(A):clone().Parent = game.Workspace
        Lighting.Brightness = 0.001
        Lighting.OutdoorAmbient = Color3.new(255/255, 255/255, 255/255)
        Lighting.ShadowColor = Color3.new(255/255, 255/255, 255/255)
        Lighting.FogColor = Color3.new(255/255, 255/255, 255/255)
        Lighting.FogEnd = 150
        Lighting.FogStart = 0
        wait (10) --Back normal
        Lighting.Brightness = 1
        Lighting.OutdoorAmbient = Color3.new(127/255, 127/255, 127/255)
        Lighting.ShadowColor = Color3.new(178/255, 178/255, 183/255)
        Lighting.FogColor = Color3.new(75/255, 75/255, 75/255)
        Lighting.FogEnd = 3000
        Lighting.FogStart = 0
        b = Players.PlayerGui:findFirstChild("GuiAA"):Destroy()
        game.Workspace:FindFirstChild(A):Destroy()
        wait(2)
    end
end