Calling an animation asset return a "Forbidden" error?

From this code:

Warrior = {game.Workspace.ClassChoose.WarriorSet.WarriorDummy, 15, 7, 371805980, BrickColor.new("Really red"), "Head"}
Classes = {Wizard, Warrior, Thief}
function Choose(Class)
	local anim = Instance.new("Animation")	
	anim.Parent = Classes[Class][1]	
	anim.AnimationId = ("http://www.roblox.com/Asset?ID="..Classes[Class][4])	
	local animController = Instance.new("AnimationController")
	animController.Parent = Classes[Class][1]
	local animTrack = animController:LoadAnimation(anim)
	print "Animation loaded"
	animTrack:Play()

This is the error:

22:46:42.957 - httpGet http://assetgame.roblox.com/asset/?id=371805980&serverplaceid=371319258 failed. Trying again. Error: HTTP 403 (HTTP/1.1 403 Forbidden). Elapsed time: 0.65074

22:46:43.607 - Content failed for http://assetgame.roblox.com/asset/?id=371805980&serverplaceid=371319258 because HTTP 403 (HTTP/1.1 403 Forbidden)

22:46:43.608 - Content failed because HTTP 403 (HTTP/1.1 403 Forbidden)

22:46:43.608 - Animation failed to load :

Workspace.ClassChoose.WarriorSet.WarriorDummy.Animation