Error that seems to be "Incorrect"?

I am trying to make a shop for a simplistic banking system. Every time I test it (by creating a test server) the shop won't open due to this error:

"Shop is not a valid member of ScreenGui"

Script 'Players.Player1.PlayerGui.Cash.ShopButton.LocalScript', Line 2

Above ^ is where the code is found inside the local player, but can also be found through

game.StarterGui.Cash.ShopButton.LocalScript

However, it is a child of the ScreenGui, there is no possible way that it is not. Why does it do that?

The code in the Script of which the error occurred in;

ShopB = script.Parent
Shop = game.Players.LocalPlayer.PlayerGui.Cash.Shop

ShopB.MouseButton1Click:connect(function()
	if Shop.Visible == false then
		Shop.Visible = true
		ShopB.Parent.BankFrame.Visible = false
	else
		Shop.Visible = false
		if ShopB.Parent.OpenBank.Text == "Close Bank" then
		ShopB.Parent.BankFrame.Visible = true
		end
	end
end)

Keep in mind: The "Shop" is a Frame. The ScreenGui is named "Cash"

Thanks for the help!

Often times, the script loads before the actual instances you're trying to retrieve have loaded. To prevent this, use the WaitForChild function to define them!

Also, since the Visible property of a gui returns a bool, then you can use the not operator on it to 'toggle' the bool. This way false becomes true and true becomes false. So just do gui.Visible = not gui,Visible(:

ShopB = script.Parent
Shop = game.Players.LocalPlayer.PlayerGui.Cash:WaitForChild('Shop')

ShopB.MouseButton1Click:connect(function()
	ShopB.Visible = not ShopB.Visible
	Shop.Visible = not Shop.Visible
end)