ScreenGui is not a valid member of UnionOperation?

whenever i click on a part after i destroyed another part i get the error 17:22:30.359 - ScreenGui is not a valid member of UnionOperation

17:22:30.359 - Stack Begin

17:22:30.360 - Script 'Players.world_kiIIer.Backpack.Tool.LocalScript', Line 7

17:22:30.360 - Stack End

this is my tool script(local script ofcourse)

local plr = game:GetService("Players").LocalPlayer

local mouse = plr:GetMouse()



script.Parent.Activated:Connect(function()

mouse.Button1Down:connect(function()

if not mouse.Target then return end

mouse.Target.ScreenGui.Parent = plr.PlayerGui

end)

end)

this is my part script also a local script

debounce = false

script.Parent.MouseButton1Click:Connect(function()

if not debounce then

debounce = true

script.Parent.BackgroundColor3 = Color3.new(255, 0, 0)

game.Workspace.ores.Modelore.ironore3.Health.Value = game.Workspace.ores.Modelore.ironore3.Health.Value - 25

wait(1)

script.Parent.BackgroundColor3 = Color3.new(0, 0, 255)

debounce = false

end

if game.Workspace.ores.Modelore.ironore3.Health.Value == 0 then

game.Workspace.ores.Modelore.ironore3.Parent = script.Parent.Parent.Parent.Parent.Backpack

script.Parent.Parent:Destroy()

end

end)

after one part has been destroyed nothing happens but when i click on another part i get the error, why? and what does it mean