[SOLVED] HP Bar works in Studio but not on Play?

I made a working health bar that decreases with the player's health, and it works perfectly on Studio, but it does not respond on Play mode. Any ideas what I am doing wrong?

PD : It is under a LocalScript...

Code :

player = game.Players.LocalPlayer
char = player.Character
human = char.Humanoid
HP = script.Parent

while wait() do
    HP:TweenSize(UDim2.new(0, (human.Health*311)/human.MaxHealth, 0, 24))
    if HP.Size.X.Offset <= 165 and HP.Size.X.Offset > 25 then
        HP.BackgroundColor3 = Color3.new(200/255, 200/255, 0)
    else if HP.Size.X.Offset <= 25 then
        HP.BackgroundColor3 = Color3.new(200/255, 0, 0)
    else
        HP.BackgroundColor3 = Color3.new(110/255, 185/255, 20/255)
    end
    end
end

Any help is appreciated!

TheArmoredReaper