c# - Only one usage of each socket address (protocol/network address/port) is normally permitted?

Question

I've been looking for a serious solution on google and i only get "Regisrty solutions" kind of stuff which i don't think even relate to my problem.

For some reason i get this Error, while i'm only starting the TcpListner once, and when+if fails i stop the server. I really don't get it. Here is my code:

class Program
    {
        private static string ServerName = "";
        private static string UserName = "";
        private static string Password = "";
        private static string dbConnectionSring = "";
        private static X509Certificate adminCertificate;
        private  static byte[] readBuffer = new byte[4096];
        static void Main(string[] args)
        {
            Console.WriteLine("Please grant SQL Server access to the Admin Server:
");
            Console.Write("Server Name: ");
            ServerName = Console.ReadLine();
            Console.Write("
User Name: ");
            UserName = Console.ReadLine();
            Console.Write("
Password: ");
            Password = PasswordMasker.Mask(Password);
            dbConnectionSring = SQLServerAccess.CreateConnection(ServerName, UserName, Password);
            adminCertificate = Certificate.GenerateOrImportCertificate("AdminCert.pfx", "randomPassword");
            try
            {
                Console.WriteLine("Initializing server on the WildCard address on port 443...");
                TcpListener listener = new TcpListener(IPAddress.Any, 443);
                try
                {
                    Console.WriteLine("Starting to listen at {0}: 443...", IPAddress.Any);

                    //the backlog is set to the maximum integer value, but the underlying network stack will reset this value to its internal maximum value
                    listener.Start(int.MaxValue);
                    Console.WriteLine("Listening... Waiting for a client to connect...");
                    int ConnectionCount = 0;

                    while (true)
                    {
                        try
                        {

                            listener.BeginAcceptTcpClient(new AsyncCallback(AcceptCallback), listener);
                            ConnectionCount++;
                            Console.WriteLine(
                                " Accepted connection #" + ConnectionCount.ToString());


                        }
                        catch (SocketException err)
                        {
                            Console.WriteLine("Accept failed: {0}", err.Message);
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Listening failed to start.");
                    listener.Stop();

                    Console.WriteLine(ex.Message);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Initialiazing server Failed.");
                Console.WriteLine(ex.Message);
            }
        }

I will really appreciate your help!

Answer 1

1. I opened CMD and typed in : netstat -a
2. I took a look in the Local Address column.
3. I took a look at the port portion.
4. I saw that the port in my program is already active( in use ) in another program.

5. I changed my port in my program to something else.

   It Worked!

   Big thanks to: @DavidSchwartz, @Gusman