Next arrow will work JUST FINE but then back arrow is unresponsive, how do I get it to work?

I'm making a selection gui that goes forward and back but the gui keeps glitching out. I'm trying to change a value to know what the next gui is and the old one to not be visible anymore. Can anyone help? It will NOT go back at all but it goes next. Next:

--next
	local gui= script.Parent.Parent.Flights


script.Parent.MouseButton1Click:connect(function()


local old= gui.Old.Value
	local gui= script.Parent.Parent.Flights
	local max= gui.Max.Value
	local min= gui.Min.Value
	local now= gui.Current.Value
	local flights= gui.Flights
	script.now.Value= script.now.Value+1
	gui.Current.Value= script.now.Value
	print(now)
	
	if now > max then
old= now-1
		script.now.Value= min
	now= script.now.Value
			print("bad")
		local curfli= flights:FindFirstChild("F"..now)
		local oldfli= flights:FindFirstChild("F"..old)
			if oldfli orcurfli ~= nil then
		curfli.Visible=true
		oldfli.Visible=false
			script.Parent.Parent.Page.Text= now.." / "..max			
end
	elseif now > min or now == min  then
	print("good")
old= now-1
		local curfli= flights:FindFirstChild("F"..now)
		local oldfli= flights:FindFirstChild("F"..old)
			if oldfli or curfli ~= nil then
		curfli.Visible=true
		oldfli.Visible=false
script.Parent.Parent.Page.Text= now.." / "..max		
end
	end
	
	
end)

Back:

--back
	local gui= script.Parent.Parent.Flights


script.Parent.MouseButton1Click:connect(function()
local old= gui.Old.Value
	local gui= script.Parent.Parent.Flights
	local max= gui.Max.Value
	local min= gui.Min.Value
	local now= gui.Current.Value
	local flights= gui.Flights
	now= now-1
	
	print("new"..now)
	print("old"..old)
if now == 0 or now > max then
	print("NO")
	
	now= 1
	old= 2	
		local oldf= flights:FindFirstChild("F"..old)
	local nowf= flights:FindFirstChild("F"..now)
		if oldf or nowf ~= nil then
	script.Parent.Parent.Page.Text= now.." / "..max	
	oldf.Visible=false
	nowf.Visible=true	
	end
else
	old= now+1
	print("ya")
	local oldf= flights:FindFirstChild("F"..old)
	local nowf= flights:FindFirstChild("F"..now)
	if oldf or nowf ~= nil then
	oldf.Visible=false
	nowf.Visible=true
	script.Parent.Parent.Page.Text= now.." / "..max		
	end
end
end)