Why does roblox say that this isnt a child of the script?

i am trying to change default roblox animations, and roblox keeps saying that walk is not a child of the animation script

here is my code:

game.Workspace.RemoteEvent.OnServerEvent:connect(function(player)
    print("got it")
player.Character.Humanoid.WalkSpeed = 35
player.Character.Animate.walk.WalkAnim.AnimationId = "http://www.roblox.com/asset?id=311043677"


end)

this is fired through an remote event when the player presses and holds the shift button. I read on the wiki, and it said that u have to do it like that, so i dont understand what im doing wrong

is it my code or a roblox bug