Why does tweening this make it look goofy?

II cannot get this gui to tween properly.

Error in output: Can only tween objects in the workspace (line 26)

local sign = script.Parent
local click = sign.ClickDetector


click.MouseHoverEnter:connect(function(player)
	print("Hovered")
    
	local signgui = Instance.new("BillboardGui",script.Parent)
    
	signgui.Size = UDim2.new(4,0,2,0)
	signgui.SizeOffset = Vector2.new(-0.5,3)
	signgui.AlwaysOnTop = true
	
    local signgui1 = Instance.new("TextLabel",signgui)
    
	signgui1.Size = UDim2.new(2,0,2,0)
	signgui1:TweenPosition(UDim2.new(-0.5,0,-3,0), "In", "Quad", 3)
	wait(0.5)
	signgui1:TweenPosition(UDim2.new(0.5,0,3,0), "Out", "Quad", 3)
	signgui1.Text = "Welcome, " .. player.Name .. ", to Land of Guardia by Nathen35."
	signgui1.TextScaled = true
	signgui1.TextWrapped = true
	
	click.MouseHoverLeave:connect(function(player)
		signgui1:TweenPosition(UDim2.new(-0.5,0,-3,0), "In", "Quad", 2)
		wait(3)
		signgui:Destroy()
	end)
end)