Similar to kaalikas comments on Send(), the asynchronous version BeginSend() actually excepts with an ArgumentException if the size of the data is zero. This should not be the case since for example the FTP protocol needs to send zero size data packets to signify a directory is empty after sending a LIST command.

I've commented out the lines below and everything works as expected now. Notice that the definition of the Socket class in MSDN explicitly says that an exception will only occur if size < 0 precisely because the reason given above.

Cheers!
AL

---- Modified BeginSend()------
public override IAsyncResult BeginSend(byte[] buffer, int offset, int size, SocketFlags socketFlags, AsyncCallback callback, object state) {
if (SecureProtocol == SecureProtocol.None)
return base.BeginSend(buffer, offset, size, socketFlags, callback, state);
if (!Connected)
throw new SocketException();
if (buffer == null)
throw new ArgumentNullException();
// if (size == 0)
// throw new ArgumentException();
if (offset < 0 || offset >= buffer.Length || size > buffer.Length - offset || size < 0)
throw new ArgumentOutOfRangeException();
// begin secure send
return m_Controller.BeginSend(buffer, offset, size, callback, state);
}