Why does this script not work in a play mode?

It's a server script inside of a module script that is placed in Startergui It works in test solo but not in play FE is on

--Pieces
repeat wait() until script.Parent.Parent.Parent.Parent
wait(.5)
script.Parent.Parent.WelcomeScreen.Welcome:TweenPosition(UDim2.new(0.35, 0,.4, 0),"InOut","Elastic",2.6,false)
local Player = script.Parent.Parent.Parent
local Mouse = Player:GetMouse()
local slab = script.Parent.Parent.Refrences.Slab:Clone()

script.Parent.Parent.WelcomeScreen.Welcome.Enter.MouseButton1Down:connect(function()
    script.Parent.Parent.WelcomeScreen.Welcome:TweenPosition(UDim2.new(0.35, 0,-.25, 0),"InOut","Linear",.6,false)
    wait(.5)
--  script.Parent.Parent.WelcomeScreen.Loading:TweenPosition(UDim2.new(0, 0,-.2, 0),"InOut","Linear",.6,false)
--  wait(3)
--  script.Parent.Parent.WelcomeScreen.Loading:TweenPosition(UDim2.new(0, 0,2, 0),"InOut","Linear",.6,false)
end)

Mouse.Button1Down:connect(function()
    if script.Parent.Parent.MaterialPicker.Placing.Value == true then
        if script.Parent.Parent.MoneyDisplay.PartCount.Count.Value ~= 800 then
        wait(.1)
        local SlabClone = Player.Character.Slab:Clone()
        SlabClone.Parent = game.Workspace
        SlabClone.Transparency = 0
        SlabClone.CanCollide = true
--      script.Parent.Parent.MoneyDisplay.PartCount.Count.Value = script.Parent.Parent.MoneyDisplay.PartCount.Count.Value + 1
--      script.Parent.Parent.MoneyDisplay.PartCount.TextLabel.Text =  script.Parent.Parent.MoneyDisplay.PartCount.Count.Value.."/800"
        end
    end
end)

round = function(N,D) 
    return math.floor((N/(D or 1))+0.5)*(D or 1) 
end 

while true do
    wait(.1)
    if script.Parent.Parent.MaterialPicker.Placing.Value == true then
        slab.Parent = Player.Character
        slab.Transparency = .6
        local material = script.Parent.Parent.MaterialPicker.MainFrame.CurrentMaterial.Value
        local x = math.ceil(Mouse.Hit.p.X)-2
        local z = math.ceil(Mouse.Hit.p.Z)-2
        x1 = x%4
        z1 = z%4
        x2 = x + (4 - x1)
        z2 = z + (4 - z1)
        slab.CFrame = CFrame.new(x2,round(Mouse.Hit.p.Y,.1)+.3,z2)
        slab.Material = Enum.Material[material]
        slab.CanCollide = false
    else
        slab.Transparency = 1
    end