Why does this only work in Test mode? [ADDED SCRIPT :D]

Hi, I'm making a One Piece game- a Anime-based game. And I already made the Data. Now every time someone spawns into my game, a GUI will pop up on their screen. My problem is that it only works in ROBLOX studio. i.e, when I'm testing it. It even changes the StringValue in the Data. And it's supposed to clone a tool in the lighting, and deliver it to my Backpack. As I said, it works fine in Studio. It's when I play the game in a server.

KS = script.Parent
ScreenGui = script.Parent.Parent
StarterGui = script.Parent.Parent.Parent
local Player = game.Players.LocalPlayer
mouse = Player:GetMouse()
function DataClone(mouse)
    LKS = game.Lighting.KnightsSword:clone()
    LKS.Parent = Player.Backpack
    Player.Data.Weapon.Value = "KS"
dope = ScreenGui:GetChildren()
for i, v in pairs(dope) do
    v:Remove()
end
end
script.Parent.MouseButton1Click:connect(DataClone)