System.InvalidOperationException: 'There is already an open DataReader associated with this Connection which must be closed first.'

Question

My application is MVC 3.1. I'm not sure what could be the reason for "System.InvalidOperationException". Any help is appreciated!

public dynamic MostBoughtItems()
{
    return _orderRepository.MostBoughtItems();
}

//Repository _orderRepository:

public dynamic MostBoughtItems()

    {
        return _DbContext.Orders.GroupBy(x => x.ItemTitle, x => x.Quantity).Where(g => g.Count() > 1).OrderByDescending(g => g.Count()).Select(g => g.Key).Take(3);
    }
    

public List<MenuItem> GetTopTreeMenuItems()
    {
        List<MenuItem> topMenuItems = new List<MenuItem>();
        var threeFav = MostBoughtItems();
        
        foreach(var item in threeFav)
        {
            string title = Convert.ToString(item);
            var singleItem = _menuItemService.GetMenuItemByTitle(title);
            topMenuItems.Add(singleItem);
        }
        return topMenuItems;
    }

// Here is the line where the error shows:

public MenuItem GetMenuItemByTitle(string itemTitle)
{
    return _DbContext.MenuItems.FirstOrDefault(x => x.Title.Contains(itemTitle));
}