1) Yes, use dot notation Ip address, but not host name. 
2)Yes, and the local port is 502,Fixed and do not need the OS to select anymore. 
3) Timeout set is 200ms, i thinkit's not the problem, because ever i set this to 5000ms, but still, ths error occured. I just don't know why. 
4) No, i have not check this. The communication is from the PC to a module we need to control, but not another PC. Anyway i didn't try this. 
I've attached the picture. Thanks for your reply. 
 
Hi MikaelH, 
Thanks for your reply. 
You can see my reply picture? 
The error occured at the TCP/IP open stage, and nerver sent strings, so you mean when i excute the TCP open function i can check the  
network bytes by some other tools? 
Tom