Directory services not always working when finding network machines

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C#

Hi
I have some code on a small project where I want to find all the machines on my network. I need to ultimately get the hostnames and currently, I use Directory Services and then drill down to the child entries to find the information I need. This has worked great for about a year on multiple machines on different networks.

I have started to find though that more and more machines are not finding anything even though explorer will see them fine. I even think machines which previously found things now don't so I'm wondering if this is a windows update which has left me in trouble.

My question therefore is has anyone else experienced this and if so is there a resolution? Is there something better to use than Directory Services (i did use to find it a little slow anyway)

private void GetMachines()//(object sender, EventArgs e)
       {

           string MachineDetails;
           int MachineCheckBox = 0;
           string MyMachineName = Environment.MachineName;

           if (System.Net.Dns.GetHostName().Length < 16)
           {
               System.Net.Dns.GetHostName().ToString();
           }
           else
           {
               System.Net.Dns.GetHostName().Substring(0, 15).ToUpper();
           }

           DirectoryEntry root = new DirectoryEntry("WinNT:");
           foreach (DirectoryEntry computers in root.Children)
           {
               foreach (DirectoryEntry computer in computers.Children)
               {
                   string ComputerName = computer.Name;
                   if ((computer.Name != "Schema") && (ComputerName != MyMachineName))// "Composer_A"))
                   {

                       MachineCheckBox = MachineCheckBox + 1;

                       CheckBox box;

                       MachineDetails = computer.Name;// +"\r\n";
                       box = new CheckBox();
                       IPAddress[] ipaddress = Dns.GetHostAddresses(ComputerName);
                       foreach (IPAddress ip4 in ipaddress.Where(ip => ip.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork))
                       {
                           box.Tag = ip4;
                       }
                       System.Net.Dns.GetHostAddresses(ComputerName);


                       box.Text = MachineDetails;
                       box.Checked = true;
                       box.AutoSize = true;
                       box.Location = new Point(10, MachineCheckBox * CheckBoxSpacing); //vertical
                       //box.Location = new Point(i * 50, 10); //horizontal
                       //this.Controls.Add(box);
                       grpMachines.Controls.Add(box);

                   }
               }
               int groupwidth = grpRemovableDrives.Size.Width;
               int grpMachinesHeight = grp1stControl + (MachineCheckBox * CheckBoxSpacing);
               if (grpMachinesHeight < 36)
               {
                   grpMachinesHeight = 36;
               }
               grpMachines.Size = new Size(groupwidth, grpMachinesHeight);
               this.Size = new Size(this.Size.Width, (grpMachines.Location.Y + grpMachines.Size.Height) + 50);

           }
       }

What I have tried:

Stepping through there are no errors just the count = 0 under the child. on my test system windows explorer shows 3 machines all with working shares (if shares makes a difference)