[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