[Fixed] Invalid table key type used?

Hello, im trying to get an inventory system i made for a game to save but it only works about 50% of the time and the other 50% it gives me the error: "Invalid table key type used" when the local script fires the remote event or if using sever side scripts to bypass the remote event when it is saving. Here is one of the tables that the inventory script sends to the sever that causes the error

	{{nil,nil,0,nil},{nil,nil,nil,nil},{nil,nil,nil,nil},{nil,nil,nil,nil},{nil,nil,nil,nil}}

(when there is a nil there is no item when there is a number there is an item. Items are saved as an ID so that's why there is an number.)

scrips that get errors:

The first one (Client sided)

	function module.Moveitem(Row,SlotID,plr)
	local ROW = Inventory[Row]
	local IMGID = game.ReplicatedStorage.Items[ROW[SlotID]].ImageID.Value
	if ROW[SlotID] ~= nil then
		script.MouseDown.Value = true
		repeat wait(0.1) until script.MouseDown.Value == false
		if Inventory[LatestHover.X][LatestHover.Y] == nil then
			Inventory[LatestHover.X][LatestHover.Y] = ROW[SlotID]
			local IMGROW = script.Parent.Contens["Row" .. LatestHover.X]
			IMGROW[LatestHover.Y].Image = "rbxassetid://" .. IMGID
			IMGROW[LatestHover.Y].ImageTransparency = 0
			IMGROW = script.Parent.Contens["Row" .. Row]
			IMGROW[SlotID].ImageTransparency = 1
			ROW[SlotID] = nil
			---- Inventory = {{nil,nil,0,nil},{nil,nil,nil,nil},{nil,nil,nil,nil},{nil,nil,nil,nil},{nil,nil,nil,nil}}
			game.ReplicatedStorage.Remoteevents.SaveItems:FireServer(Inventory) --- this line has the error
		end
	end
end

the script that handels the Remote event (Sever side form this point on):

game.ReplicatedStorage.Remoteevents.SaveItems.OnServerEvent:Connect(function(plr,inv)
	local AACI = require(game.ServerScriptService.AAC.Inventory[plr.Name])
	AACI.GetInventory(inv)
end)

The part of the script that the Remote event uses

	function module.GetInventory(Inv)
		print("Setting")
		Inventory = Inv
	end

The part that saves

	function module.SaveToSever(plr)
	print("Saving Inventory")
	local DataStoreService = game:GetService("DataStoreService")
	local Inventory_ = DataStoreService:GetDataStore("Inventory")
	local Item = DataStoreService:GetDataStore("Items")
	local key = "user_"..plr.userId
	Item:SetAsync(key,Items)
	for ROWID = 1,5 do
		local Row = Inventory[ROWID]
		for SLOTID = 1,4 do
			if Row[SLOTID] ~= nil then
				local HasItem = false
				local ITEMID = Row[SLOTID]
				for i,v in pairs(Items) do
					if v[1] == ITEMID then
						if v[3]+1 <= v[2] then
							v[3] = v[3] +1
							HasItem = true
						end
					end
				end
				if HasItem == false then
					Row[SLOTID] = nil
				end
			end
		end
	end
	Inventory_:SetAsync(key,Inventory)
end

I changed nil to "nil" and that solved the problem.