It is AIR apps. Anyway, after I set the server to listen to IP 0.0.0.0, it works now.
Btw, Is it possible for Flash / AIR to do socket asynchronism / parallel flush socket? Because I want the server to send command to 5 - 6 PCs at the sametime to start a video playback and have the video sync on every PCs. Therefore, sending out command at the same time is really important. Thanks.