Info is not a valid member of ScreenGui, even though it is?

The problem is that it is looking for this info before it is even loaded yet, to solve this you need to use :WaitForChild()

local Player = game.Players.LocalPlayer
local Menu = script.Parent
local Play = Menu:WaitForChild("Play")
local About = MenuWaitForChild("About")
local HasPressedPlay = false
local info = Menu:WaitForChild("info")
local Minimize = info:WaitForChild("Minimize")
local Back = Menu:WaitForChild("Backing")

function MouseEnterPlayButton()
    Play.FontSize = "Size60"

end




function MouseLeftPlayButton()
    Play.FontSize = "Size36"


end





function MouseEnterAboutButton()
    About.FontSize = "Size60"

end




function MouseLeftAboutButton()
    About.FontSize = "Size36"


end




function PlayGame()
    if HasPressedPlay == false then
        for i = 1, 40 do
            if i <= 20 then
            Play.Position = Play.Position + UDim2.new(0.05, 0, 0, 0)
            end
            if i >= 10 then
                About.Position = About.Position + UDim2.new(0.05, 0, 0, 0)
                Menu.Title.Position = Menu.Title.Position + UDim2.new(0.05, 0, 0, 0)
                Menu.Version.Position = Menu.Version.Position + UDim2.new(0.05, 0, 0, 0)
            end
            if i == 40 then
                Back.Visible = false
            end
            wait()
        end
    end

end


function Minimizeinfo()
    info.Visible = false
end

function ShowAbout()
    info.Visible = true
end



About.MouseButton1Down:connect(ShowAbout)
Minimize.MouseButton1Down:connect(Minimizeinfo)
Play.MouseButton1Down:connect(PlayGame)
Play.MouseLeave:connect(MouseLeftPlayButton)
Play.MouseEnter:connect(MouseEnterPlayButton)
About.MouseLeave:connect(MouseLeftAboutButton)
About.MouseEnter:connect(MouseEnterAboutButton)


-- 27, 42, 53

Hope this helps