Diaster script not running?

I am making a new surivive the diasters and the models in lighting will not load.

disasters = {"Minotaurs!!!", "Zombies", "", "", "", ""} --Disaster names are case-sensitive and all disaster models must be in the lighting

getpoints = 100 --Points you will get after Disaster
countdownTime = 1 -- The ammount of time to wait between each disaster.
disasterTime = 100 -- The ammount of time that the disaster will be in the game before it is removed.

countdownMessage = "The next Disaster will occur in %s seconds." -- The message displayed between disasters. %s will be replaced with the number of seconds left.
WdisasterMessage = "Disaster Choosen: %s" -- The message displayed when a disaster occurs. %s will be replaced with the disaster name. Set to nil if you do not want a message
disasterTimeMessage = "The Disasters will stop in %s"

---------------------------------Don't do anything there!Only if u know how!----------------------------------------------------------------------------------------
items = {}
leaderboard = game.Workspace:findFirstChild("BTS Leaderboard") -- Used to work with my BTS leaderboard
local w = game.Workspace:getChildren()
for i=1,#w do
    if w[i].Name == "leaderboard" and w[i]:findFirstChild("running") ~= nil and w[i]:findFirstChild("points") ~= ni then
        leaderboard = w[i]
    end
end
for i=1,#disasters do
    local item = game.Lighting:findFirstChild(disasters[i])
    if item ~= nil then
        item.Parent = nil
        table.insert(items, item)
    else
        print("Error! ", disasters[i], " was not found!")
    end
end

function chooseDisaster()
    return items[math.random(#items)]
end

function sethint(text)
    local hint = game.Workspace:findFirstChild("hint")
    if (hint ~= nil) then
        hint.Text = text
    else
        print("Hint does not exist, creating...")
        h = Instance.new("Hint")
        h.Name = "hint"
        h.Text = text
        h.Parent = game.Workspace
    end
    --print("Hint set to: ", text)
end

function removeHint()
    hint = game.Workspace:findFirstChild("hint")
    if (hint ~= nil) then hint:remove() end
end

function countdown(time)
    sethint(string.format(countdownMessage, tostring(time)))
    while (time > 0) do
        wait(1)
        time = time - 1
        sethint(string.format(countdownMessage, tostring(time)))
    end
    removeHint()
    return true
end

function disaster(time)
    sethint(string.format(disasterTimeMessage, tostring(time)))
    while (time > 0) do
        wait(1)
        time = time - 1
        sethint(string.format(disasterTimeMessage, tostring(time)))
    end
    removeHint()
    return true
end

while true do
    countdown(countdownTime)

    if leaderboard ~= nil and leaderboard:findFirstChild("running") and leaderboard:findFirstChild("points") then -- For use with my BTS leaderboard.
        leaderboard.points.Value = getpoints
        leaderboard.running.Value = true
    end

    local m = chooseDisaster():clone()

    if WdisasterMessage ~= nil then
        local msg = Instance.new("Message")
        msg.Name = "WDisasterMsg"
        msg.Text = string.format(WdisasterMessage, m.Name)
        msg.Parent = game.Workspace
        wait(3)
        msg.Parent = nil
    end

    m.Parent = game.Workspace
    m:makeJoints()
    disaster(disasterTime)
    m:remove()

    if leaderboard ~= nil then -- For use with the bts leaderboard.
        leaderboard.running.Value = false
    end
end

When it starts, it says in a bold red text: 20:39:26.972 - Workspace.ZombieRoundScript:31: bad argument #1 to 'random' (interval is empty) Please help me! Thanks!