Whats wrong with the regen?

I am using xLegox's 3.0 cart track, and there is one problem, it won't regen! Here is the script.

local cartModel = script.Parent.TrainCart:clone()

local spawnButton = script.Parent.SpawnButton
local origin = script.Parent.Origin

local buttonOffColor = BrickColor.new(1007)
local buttonOnColor = BrickColor.new(1020)


function enable(cart)
	cart.Parent = game.Workspace
	cart:MakeJoints()
	cart.DriveScript.Disabled = false
end

--returns: is the space to spawn the cart in free?
function isFree()
	local origincf = origin.CFrame
	local a = (origincf*CFrame.new(-3.5, 1, -5.5)).p 
	local b = (origincf*CFrame.new(3.5, 5, 5.5)).p
	local ax, ay, az = a.x, a.y, a.z
	local bx, by, bz = b.x, b.y, b.z
	if ax > bx then ax, bx = bx, ax end
	if ay > by then ay, by = by, ay end
	if az > bz then az, bz = bz, az end
	local list = game.Workspace:FindPartsInRegion3(Region3.new(Vector3.new(ax, ay, az), Vector3.new(bx, by, bz)))
	return #list == 0
end

--enable the current cart
enable(script.Parent.TrainCart)

do
	local debounce = false
	function doSpawn()
		if not debounce and isFree() then
			debounce = true
			enable(cartModel:clone())
			wait(0.1)
			debounce = false
		end
	end
end

--set up connections
spawnButton.Touched:connect(function(obj)
	local par = obj.Parent
	if par and par:FindFirstChild("Humanoid") then
		doSpawn()
	end
end)
spawnButton.ClickDetector.MouseClick:connect(doSpawn)
--spawnButton.DoSpawn.Receive = doSpawn --requires future updates

--show open state
while true do
	wait(0.1)
	if isFree() then
		spawnButton.BrickColor = buttonOnColor
		origin.Fire.Enabled = true
	else
		spawnButton.BrickColor = buttonOffColor
		origin.Fire.Enabled = false
	end
end