Animations not playing correctly?

trying to make an idle animation for my NPCs play but it turns out only the first player that joins the server can see the animations in the NPCs, don't know what I'm doing wrong, can somebody tell me?

wait (10)
local humanoid = script.Parent:WaitForChild("Humanoid")
local anim = Instance.new("Animation")
anim.AnimationId = "http://www.roblox.com/asset/?id=248263260"

local Idle = nil

while not Idle do
Idle = humanoid:LoadAnimation(anim)
wait()
end

wait()

Idle:Play()