Why does this script crash my game?

I've made a login gui (No, not one of those. For a beta game) and when I test it, it crashed, but I don't know why.

local UName = script.Parent:WaitForChild("UName")
local UPass = script.Parent:WaitForChild("UPass")
local Attempts = script.Parent:WaitForChild("Attempts")
local Button = script.Parent:WaitForChild("Login")
local pass = {["Herro"] = true;}
local transparency = 0
local debounce = false
local warningA = "You have "
local warningB = " attempts left."
local countdown = 10
local function checkAttempts()
    if Attempts.Value == 0 then
        script.Parent.Warning.Text = "You will be kicked in "..countdown.. " seconds."
        repeat
            countdown = countdown - 1
            wait(1)
        until countdown == 0
        game.Players.LocalPlayer:Kick()
    else
        Attempts.Value = Attempts.Value - 1
        script.Parent.Warning.Text = warningA..Attempts.Value..warningB
        wait(6)
        script.Parent.Warning.Text = ""
        debounce = false
    end
end

UName.Text = game.Players.LocalPlayer.Name

Button.MouseButton1Click:connect(function()
    if debounce == false then
        debounce = true
        if pass[UPass.Text] then
            repeat
                script.Parent.Parent.Parent.Parent.BackgroundTransparency = script.Parent.Parent.Parent.Parent.BackgroundTransparency + 0.05
                script.Parent.Parent.Parent.Parent.Frame.BackgroundTransparency = script.Parent.Parent.Parent.Parent.Frame.BackgroundTransparency + 0.05
                script.Parent.Parent.Parent.Parent.Frame.LittleRedBar.BackgroundTransparency = script.Parent.Parent.Parent.Parent.Frame.LittleRedBar.BackgroundTransparency + 0.05
                script.Parent.Parent.Parent.Parent.Frame.Frame.BackgroundTransparency = script.Parent.Parent.Parent.Parent.Frame.BackgroundTransparency  + 0.05
                transparency = transparency + 0.05
            until transparency == 1
        else
            checkAttempts()
        end
    end
end)

If possible, how would I also make it more efficient?