attempt to index nil with 'Item' Help?

I have a inventory gui that I am making so you can move to "Sort" your inventory. It will not work, It always errors. Here is the script (Normal script inside text button):

local MovingInventory = script.Parent.Parent.Parent.Parent.Parent.MovingInventory
local SlotMoving = script.Parent.Parent.Parent.Parent.Parent.MovingInventory

script.Parent.MouseButton1Click:Connect(function()
    if MovingInventory.Value == false then
        MovingInventory.Value = true
        SlotMoving.Value = script.Parent.Name
    elseif MovingInventory.Value == true then
        MovingInventory.Value = false
        game.ReplicatedStorage.Values:WaitForChild("Item").Value = script.Parent.Parent:FindFirstChild(SlotMoving.Value).Item.Value
        game.ReplicatedStorage.Values:WaitForChild("Amount").Value = script.Parent.Parent:FindFirstChild(SlotMoving.Value).Amount.Value
        script.Parent.Item.Value = script.Parent.Parent:FindFirstChild(SlotMoving.Value).Item.Value
        script.Parent.Amount.Value = script.Parent.Parent:FindFirstChild(SlotMoving.Value).Amount.Value
        script.Parent.Parent:FindFirstChild(SlotMoving.Value).Item.Value = game.ReplicatedStorage.Values.Item.Value
        script.Parent.Parent:FindFirstChild(SlotMoving.Value).Amount.Value = game.ReplicatedStorage.Values.Amount.Value
    end
end)

Thanks!

Your script errors, as one of your FindFirstChild returns nil, meaning it has not found what you tasked it with finding. Which one exactly is erroring, I cannot say, as you did not provide your output and which line is causing issues. What I can suggest though, is to clean up your code a bit:

local MovingInventory = script.Parent.Parent.Parent.Parent.Parent.MovingInventory
local SlotMoving = script.Parent.Parent.Parent.Parent.Parent.MovingInventory
local Item =  game.ReplicatedStorage.Values:WaitForChild("Item")
local Amount = game.ReplicatedStorage.Values:WaitForChild("Amount")

script.Parent.MouseButton1Click:Connect(function()
    if MovingInventory.Value == false then
        MovingInventory.Value = true
        SlotMoving.Value = script.Parent.Name
    elseif MovingInventory.Value == true then
	local Slot = script.Parent.Parent:FindFirstChild(SlotMoving.Value)
	if not Slot then
		warn("Slot not found")
		return
	end
        MovingInventory.Value = false
        Item.Value =Slot.Item.Value
        Amount.Value = Slot.Amount.Value
        script.Parent.Item.Value =Slot.Item.Value
        script.Parent.Amount.Value = Slot.Amount.Value
        Slot.Item.Value = Item.Value
        Slot.Amount.Value = Amount.Value
    end
end)

Hope this helps.