Says Ba isn't valid member of StarterGui?

It works in studio but in game it doesn't. When I check what was wrong in game, it said Ba wasn't a valid member of StarterGui.

Here is script.

local Back2 = script.Parent.Ba
local BarHold = script.Parent.BarFrame
local Loadbar = script.Parent.BarFrame.barLoad
local LogoSp = script.Parent.LogoSpin
local Nam = script.Parent.BoiNOi
local PlayBut = script.Parent.PleyBut
local barloading = false
local canSpin = false
local blr = game.Lighting.Blur
local canPlay = false
blr.Size = 50



function playClicked()
    Nam.TextTransparency = 1
    PlayBut.TextTransparency = 1
    Nam:TweenPosition(UDim2.new(0.329, 0,-2, 0),"In","Quad",1.5)
    PlayBut:TweenPosition(UDim2.new(0.455, 0,1, 0),"In","Quad",1.5)
    wait(1)
    Back2:Remove()
        for g =  50,0,-5 do
            wait(.01)
            blr.Size = (g)
        end
end

function onStart()
    repeat wait() until Back2
    if Back2 then 
        print("HERE")
    end 
    blr.Size = 56
    Nam.TextTransparency = 1
    PlayBut.TextTransparency = 1
    LogoSp.ImageTransparency = 1
    LogoSp:TweenPosition(UDim2.new(0.403, 0,0.302, 0),"In","Quad",.5)
    PlayBut:TweenPosition(UDim2.new(0.455, 0,1, 0),"In","Quad",1.5)
    Nam:TweenPosition(UDim2.new(0.329, 0,-2, 0),"In","Quad",.5)
    Back2.Position = UDim2.new(0,0,0, 0)
    Loadbar.Size = UDim2.new(0, 4,0, 35)
    wait(.1)
    barloading = true 
        if barloading == true then
            repeat wait() until Loadbar
            wait(.1) 
            Loadbar:TweenSize(UDim2.new(0, 111,0, 35),"Out","Quad",1)
            wait(1)
            Loadbar:TweenSize(UDim2.new(0, 248,0, 35),"Out","Quad",1)
            wait(1.5)
            Loadbar:TweenSize(UDim2.new(0, 427,0, 35),"Out","Quad",1)
            barloading = false
        end
        wait(2)
        BarHold:TweenPosition(UDim2.new(1, 0,0.85, 0),"Out","Quad",1)
        wait(2)
    if barloading == false then
        canSpin = true 
        print("Can spin = true")
            if canSpin == true then
                repeat wait() until LogoSp
                    print("about to spin")
                    LogoSp.ImageTransparency = 0
                    for i = 1,120,1 do
                        wait(0.01)
                        LogoSp.Rotation = LogoSp.Rotation + 20
                            if i == 120 then
                                canSpin = false
                                repeat wait() until LogoSp and Nam and PlayBut
                                LogoSp.Rotation = 0
                                wait(1)
                                LogoSp:TweenSize(UDim2.new(0, 121,0, 123),"In","Quad",1)
                                LogoSp:TweenPosition(UDim2.new(0.437, 0,0.37, 0),"In","Quad",1)
                                wait(2)
                                LogoSp:TweenPosition(UDim2.new(0.403, 0,1, 0),"Out","Quad",1)
                                wait(2)
                                Nam.TextTransparency = 0
                                Nam:TweenPosition(UDim2.new(0.329, 0,0, 0),"In","Quad",1.5)
                                wait(1)
                                PlayBut.TextTransparency = 0
                                PlayBut:TweenPosition(UDim2.new(0.455, 0,0.478, 0),"In","Quad",1.5)
                                canPlay = true
                                    if canPlay == true then
                                         if Nam.TextTransparency == 0 and PlayBut.TextTransparency == 0 then
                                        PlayBut.MouseButton1Click:connect(playClicked)

                                        end
                                    end
                            end
                    end
            end

    end
end


onStart()