problem when using GetFtpConnection from the CInternetSession class

Hello every one, I have a problem when i call GetFtpConnection method from CInternetSession class, I call it as follows:

////////////////////////////////////////////////

CInternetSession netSession;

CFtpConnection *pFtp;

CString SERVER_IP = "158.10.25.6";

int PORT = 5000;

TRY

{

pFtp = netSession.GetFtpConnection(SERVER_IP,"user","pass",PORT);

}

CATCH (CInternetException,ex)

{

char szError[100];

memset(szError,0,100);

ex->GetErrorMessage(szError,100);

AfxMessageBox(szError);

}

END_CATCH

////////////////////////////////////////////////

some times it successfully connected to the FTP server, but at some times it throw an exception told me that "Computer is disconnected from the network" , i don't know why however both the FTP server is on and connected to the network and also the client which contains this code is also on and connected to the network, so from where this error.

Can you help me please, any help will be greatly appreciated.

thank you