Use the SocketException.ErrorCode property to obtain the specific error code. When you have obtained this code, you can refer to the Windows Sockets version 2 API error code documentation in MSDN for a detailed description of the error.
Stop closes the listener. Any unaccepted connection requests in the queue will be lost. Remote hosts waiting for a connection to be accepted will throw a SocketException. You are responsible for closing your accepted connections separately.
The Stop method also closes the underlying Socket, and creates a new Socket for the TcpListener. If you set any properties on the underlying Socket prior to calling the Stop method, those properties will not carry over to the new Socket.