Folder Permissions c#

Hi, I've got some code to change the folder permissions.
The code will add the user, but when I check the permissions they haven't changed.
The following is the code.
Can anyone help, thanks.
P.S.
I had to add the references System.Management and System.Management.Instrumentation from .NET controls.
I got the code from http://www.redmondpie.com/applying-permissions-on-any-windows-folder-using-c/ 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

   using System.IO;

   using System.Security.AccessControl;

   using System.Management;

  using System.Management.Instrumentation;
namespace Permissions
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();


              GetUsers();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
        private void SelectDirectorybtn_Click(object sender, EventArgs e)

     {

                // creating a new instance fot FolderBrowsingDialog 

                                    //to provide user capability to select target Folder

                FolderBrowserDialog myFolderBrowserDialog = new FolderBrowserDialog();

      

                // showing dialog

                myFolderBrowserDialog.ShowDialog();

      

                // Show the path of selected directory in our text Box 

               textBox1.Text = myFolderBrowserDialog.SelectedPath.ToString();

    }
        //http://www.redmondpie.com/applying-permissions-on-any-windows-folder-using-c/
           private void Permissionbtn_Click(object sender, EventArgs e)

    {


    }
       public void GetUsers()

     {

             // This query will query for all user account names in our current Domain

             SelectQuery sQuery = new SelectQuery("Win32_UserAccount", "Domain='" 

                             + System.Environment.UserDomainName.ToString() + "'");

      

              try

              {

                        // Searching for available Users

                         ManagementObjectSearcher mSearcher = new 

                                                        ManagementObjectSearcher(sQuery);

     

                        foreach (ManagementObject mObject in mSearcher.Get())

                        {

                                // Adding all user names in our combobox

                                comboBox1.Items.Add(mObject["Name"]);

                        }

             }

             catch (Exception ex)

             {

                        MessageBox.Show(ex.ToString());

             }

    }

       private void Permissionbtn_Click_1(object sender, EventArgs e)
       {
           // retrieving the directory information

           DirectoryInfo myDirectoryInfo = new DirectoryInfo(textBox1.Text);



           // Get a DirectorySecurity object that represents the 

           // current security settings.

           DirectorySecurity myDirectorySecurity = myDirectoryInfo.GetAccessControl();

           string User = System.Environment.UserDomainName + "\\" +

                                                      comboBox1.SelectedItem.ToString();



           // Add the FileSystemAccessRule to the security settings. 

           // FileSystemRights is a big list we are current using Read property but you 

           // can alter any other or many sme of which are:

           // Create Directories: for sub directories Authority

           // Create Files: for files creation access in a particular folder
           // Delete: for deletion athority on folder

           // Delete Subdirectories and files: for authority of deletion over 

           //subdirectories and files

           // Execute file: For execution accessibility in folder

           // Modify: For folder modification

           // Read: For directory opening

           // Write: to add things in directory

           // Full Control: For administration rights etc etc



           // Also AccessControlType which are of two kinds either “Allow” or “Deny” 

           //myDirectorySecurity.AddAccessRule(new FileSystemAccessRule(User,

           //                                FileSystemRights.Read, AccessControlType.Allow));
           //myDirectorySecurity.AddAccessRule(new FileSystemAccessRule(User,

           //                                           FileSystemRights.Write, AccessControlType.Allow));

           myDirectorySecurity.AddAccessRule(new FileSystemAccessRule(User,

                                                      FileSystemRights.FullControl, AccessControlType.Allow));

           // Set the new access settings. 

           myDirectoryInfo.SetAccessControl(myDirectorySecurity);



           // Showing a Succesfully Done Message

           MessageBox.Show("Permissions Altered Successfully");

       }
}
}

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