what is wrong with this gui script?

function goLeft()
    script.Disabled = false
    wait(.5)
    script.Parent.Parent.Right.Visible = false
    for i = 1,56  do
        script.Parent.Parent.CustomClass1.Position = script.Parent.Parent.CustomClass1.Position - Udim2.new(-.25, 0, 0, 0)
    Script.Parent.Parent.CustomClass1.Visible = false
    script.Parent.Parent.CustomClass2.Visible = true
    script.Parent.Parent.CustomClass2.Position = Udim.new(15, 0, 1.5, 0)
    for i = 1, 48 do
        script.Parent.Parent.CustomClass2.Position = script.Parent.Parent.CustomClass1.Position - Udim2.new( -.25, 0, 0, 0)
    end
    script.Parent.Visible = false
        end 
    script.Disabled = true
end
script.Parent.MouseButton1Down:connect(goLeft)

it says "Players.Player1.PlayerGui.ScreenGui.CustomClass.Left.Script:6: attempt to index global 'Udim2' (a nil value)" also for some reason it wont let me click it, i made the transparency 1 if that matters also, its a text button, all my other text buttons are clickable but not this one any idea why?