Nil, no code changes?

I'm extremely confused.. when I try to run an event that worked, like, a minute ago, it doesn't work anymore. It just goes - attempt to call a nil value (x13) and it goes higher as I click. What? There's no specific code causing this. All my code is the same as before, I haven't edited it, it just happened all of a sudden. Is this a glitch? Am I supposed to restart all of my code? Please help.

Here is my code:

function closeButton()
	script.Parent.Parent.Visible = false
end

script.Parent.MouseButton1Click:connect(closeButton) -- This code is correct.

function open()
	game.StarterGui.ScreenGui2.Frame2.Visible = true
end

script.Parent.MouseButton1Click:connect(open)

I stopped developing the game because of this issue.