The Exception is" Provides an invalid parameter" Please help me.

[C# Programming]

hi all.

//Send
private void SendMessage(string str)
{
byte[] message = Encoding.Unicode.GetBytes(str);
Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
IPAddress ip = IPAddress.Parse("224.0.0.1");
try
{
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(ip));
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 5);
}
catch (Exception e)
{
this.Text = e.Message;
//here . Exception is Provides an invalid parameter?
}
IPEndPoint ipep = new IPEndPoint(ip, 7758);
s.Connect(ipep);
s.Send(message, message.Length, SocketFlags.None);
s.Close();

}



private void RecMessage()
{
Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 7758);
s.Bind(ipep);
IPAddress ip = IPAddress.Parse("224.0.0.1");
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(ip, IPAddress.Any));
while (true)
{
byte[] b = new byte[1024];
s.Receive(b);
string str = System.Text.Encoding.ASCII.GetString(b, 0, b.Length);
this.Text = str;
}
s.Close();
}