Имя "className" не существует в пространстве имён "clr-namespace:"

<Window x:Class="WpfApp5.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

        xmlns:local="clr-namespace:WpfApp5;assembly=WpfApp5"
        mc:Ignorable="d"
        
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid local:GridHelpers.RowCount="6"
         local:GridHelpers.StarRows="5"
         local:GridHelpers.ColumnCount="4"
         local:GridHelpers.StarColumns="1,3"/>
    </Grid>
</Window>

Сам код на C# не мой, но приложу и исходную ссылку(https://rachel53461.wordpress.com/2011/09/17/wpf-grids-rowcolumn-count-properties/). В класс вроде как добавлен, перезапускал проект, компьютер, но ошибка остаётся. Если создать более намного простой класс(из 3 элементов) и обратиться к ним, то ошибка та же именно в local:

namespace WpfApp5
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class GridHelpers
    {
        #region RowCount Property

        public static readonly DependencyProperty RowCountProperty = DependencyProperty.RegisterAttached("RowCount", typeof(int), typeof(GridHelpers), new PropertyMetadata(-1, RowCountChanged));
        // Get
        public static int GetRowCount(DependencyObject obj)
        {
            return (int)obj.GetValue(RowCountProperty);
        }

        // Set
        public static void SetRowCount(DependencyObject obj, int value)
        {
            obj.SetValue(RowCountProperty, value);
        }

        // Change Event - Adds the Rows
        public static void RowCountChanged(
            DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            if (!(obj is Grid) || (int)e.NewValue < 0)
                return;

            Grid grid = (Grid)obj;
            grid.RowDefinitions.Clear();

            for (int i = 0; i < (int)e.NewValue; i++)
                grid.RowDefinitions.Add(
                    new RowDefinition() { Height = GridLength.Auto });

            SetStarRows(grid);
        }

        #endregion

        #region ColumnCount Property

        /// <summary>
        /// Adds the specified number of Columns to ColumnDefinitions. 
        /// Default Width is Auto
        /// </summary>
        public static readonly DependencyProperty ColumnCountProperty =
            DependencyProperty.RegisterAttached(
                "ColumnCount", typeof(int), typeof(GridHelpers),
                new PropertyMetadata(-1, ColumnCountChanged));

        // Get
        public static int GetColumnCount(DependencyObject obj)
        {
            return (int)obj.GetValue(ColumnCountProperty);
        }

        // Set
        public static void SetColumnCount(DependencyObject obj, int value)
        {
            obj.SetValue(ColumnCountProperty, value);
        }

        // Change Event - Add the Columns
        public static void ColumnCountChanged(
            DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            if (!(obj is Grid) || (int)e.NewValue < 0)
                return;

            Grid grid = (Grid)obj;
            grid.ColumnDefinitions.Clear();

            for (int i = 0; i < (int)e.NewValue; i++)
                grid.ColumnDefinitions.Add(
                    new ColumnDefinition() { Width = GridLength.Auto });

            SetStarColumns(grid);
        }

        #endregion

        #region StarRows Property

        /// <summary>
        /// Makes the specified Row's Height equal to Star. 
        /// Can set on multiple Rows
        /// </summary>
        public static readonly DependencyProperty StarRowsProperty =
            DependencyProperty.RegisterAttached(
                "StarRows", typeof(string), typeof(GridHelpers),
                new PropertyMetadata(string.Empty, StarRowsChanged));

        // Get
        public static string GetStarRows(DependencyObject obj)
        {
            return (string)obj.GetValue(StarRowsProperty);
        }

        // Set
        public static void SetStarRows(DependencyObject obj, string value)
        {
            obj.SetValue(StarRowsProperty, value);
        }

        // Change Event - Makes specified Row's Height equal to Star
        public static void StarRowsChanged(
            DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            if (!(obj is Grid) || string.IsNullOrEmpty(e.NewValue.ToString()))
                return;

            SetStarRows((Grid)obj);
        }

        #endregion

        #region StarColumns Property

        /// <summary>
        /// Makes the specified Column's Width equal to Star. 
        /// Can set on multiple Columns
        /// </summary>
        public static readonly DependencyProperty StarColumnsProperty = DependencyProperty.RegisterAttached("StarColumns", typeof(string), typeof(GridHelpers), new PropertyMetadata(string.Empty, StarColumnsChanged));

        // Get
        public static string GetStarColumns(DependencyObject obj)
        {
            return (string)obj.GetValue(StarColumnsProperty);
        }

        // Set
        public static void SetStarColumns(DependencyObject obj, string value)
        {
            obj.SetValue(StarColumnsProperty, value);
        }

        // Change Event - Makes specified Column's Width equal to Star
        public static void StarColumnsChanged(
            DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            if (!(obj is Grid) || string.IsNullOrEmpty(e.NewValue.ToString()))
                return;

            SetStarColumns((Grid)obj);
        }

        #endregion

        private static void SetStarColumns(Grid grid)
        {
            string[] starColumns =
                GetStarColumns(grid).Split(',');

            for (int i = 0; i < grid.ColumnDefinitions.Count; i++)
            {
                if (starColumns.Contains(i.ToString()))
                    grid.ColumnDefinitions[i].Width =
                        new GridLength(1, GridUnitType.Star);
            }
        }

        private static void SetStarRows(Grid grid)
        {
            string[] starRows =
                GetStarRows(grid).Split(',');

            for (int i = 0; i < grid.RowDefinitions.Count; i++)
            {
                if (starRows.Contains(i.ToString()))
                    grid.RowDefinitions[i].Height =
                        new GridLength(1, GridUnitType.Star);
            }
        }
    }
}