Studio into real game Error (Please Help)?

You need to use WaitForChild.

When starting up a game on a server, things load at different time. Sometimes a script loads before the things the script is trying to access. Meaning you have to wait for the things to exist. To do this, all you have to do is use WaitForChild. You don't, however, need to use WaitForChild when accessing the parent of the script. This is because the parent loads before the children. Here's what your script would look like after making the changes,

--in local script
Player = game.Players.LocalPlayer
Menu = script.Parent
Play = Menu:WaitForChild("Play")
About = Menu:WaitForChild("About")
HasPressedPlay = false
Info = script.Parent:WaitForChild("Info")
Minimize = Info:WaitForChild("Minimize")

function MouseEnterPlayButton()
    Play.FontSize = "Size36"
    Play.Size = UDim2.new(0.45, 0, 0.160, 0)
end
 
function MouseLeftPlayButton()
    --166, 166, 166
    Play.FontSize = "Size24"
    Play.Size = UDim2.new(0.3, 0, 0.15, 0)
end
 
function MouseEnterAboutButton()
    About.FontSize = "Size36"
    About.Size = UDim2.new(0.45, 0, 0.160, 0)
end
 
function MouseLeftAboutButton()
    --166, 166, 166
    About.FontSize = "Size24"
    About.Size = UDim2.new(0.3, 0, 0.15, 0)
end
 
function PlayGame()
    if HasPressedPlay == false then
        for GuiMove = 1, 30 do
            if GuiMove <= 30 then          
                    Play.Position = Play.Position +UDim2.new(0.06, 0, 0, 0)
                end
                if GuiMove <= 20 then          
                    About.Position = About.Position +UDim2.new(0.05, 0, 0, 0)  
                end
                wait()
            end
 
        Menu:remove()  
    end 
end
 
function MinimizeInfo()
    Info.Visible = false
end
 
function InfoPopup()
    if Info.Visible == false then  
        Info.Visible = true
    else
        Info.Visible = false
    end
end
 
About.MouseButton1Down:connect(InfoPopup)
Minimize.MouseButton1Down:connect(MinimizeInfo)
Play.MouseLeave:connect(MouseLeftPlayButton)
Play.MouseEnter:connect(MouseEnterPlayButton)
About.MouseLeave:connect(MouseLeftAboutButton)
About.MouseEnter:connect(MouseEnterAboutButton)
Play.MouseButton1Down:connect(PlayGame)

That looked to be the only problem. That should work. Good Luck!