LoadAnimation requires the Humanoid object to be a descendant of the game object?

local CAS = game:GetService("ContextActionService")
local UIS = game:GetService("UserInputService")
local jumpDisabled = false

local player = game.Players.LocalPlayer
local char = player.Character or player.CharacterAdded:wait()
local hum = char:WaitForChild("Humanoid")

local run_Anim = hum:LoadAnimation(script:WaitForChild("ExportAnim"))

function onJump()
    if jumpDisabled then
        hum.Jump = false
    end
end

function toggleSprint(actionName, inputState, inputObject)
    if inputState == Enum.UserInputState.Begin then
        hum:LoadAnimation(script:WaitForChild("ExportAnim")):Play()
        hum.WalkSpeed = 35 
        jumpDisabled = true
    elseif inputState == Enum.UserInputState.End then
        hum:LoadAnimation(script:WaitForChild("ExportAnim")):Stop()
        hum.WalkSpeed = 16    
        jumpDisabled = false
        hum:LoadAnimation(script:WaitForChild("WalkAnim")):Play()
    end
end


function windowFocused()
    hum:LoadAnimation(script:WaitForChild("ExportAnim")):Stop()
    hum.WalkSpeed = 16  
    jumpDisabled = false
end

CAS:BindAction("toggleSprint", toggleSprint, false, Enum.KeyCode.LeftShift)
UIS.WindowFocused:connect(windowFocused)
hum.Changed:connect(onJump)