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

LoadAnimation requires the AnimationController object (MP5.AnimationController) to be a descendant of the game object?

local Gun=game.ReplicatedStorage.GunStorage.MP5:Clone()
local Controller=Instance.new("AnimationController")
local ShootValue=game.ReplicatedStorage.GunValue.MP5:WaitForChild("ShootingAnim1").Value
local ShootAnim1 =Instance.new("Animation")
ShootAnim1.AnimationId ="rbxassetid://"..ShootValue
ShootAnim1.Parent=Gun
Controller.Parent=Gun
local LShootAnim1=Controller:LoadAnimation(ShootAnim1)

LoadAnimation requires the Humanoid object (MP5.Humanoid) to be a descendant of the game object? umm...

local Gun=game.ReplicatedStorage.GunStorage.MP5:Clone()
local GunHum=Gun:WaitForChild("Humanoid")
local Controller=Instance.new("AnimationController")
--
local ShootValue=game.ReplicatedStorage.GunValue.MP5:WaitForChild("ShootingAnim1").Value
local ShootAnim1 =Instance.new("Animation")
ShootAnim1.AnimationId ="rbxassetid://"..ShootValue
--
ShootAnim1.Parent=Gun
Controller.Parent=Gun
local LShootAnim1=GunHum:LoadAnimation(ShootAnim1)

Basically you forgot to parent the animation on line 6

local ShootAnim1 =Instance.new("Animation")
ShootAnim1.AnimationId ="rbxassetid://"..ShootValue
ShootAnim1.Parent = gun
-- Parent the animation?

The animations do need to be in the game for them to work

Another EDIT

The more I look at yours it makes me think because I don't think you can load animations onto a object that isn't in workspace.