FTP transfer with 425 can't open data connection error".

In our application we are trasnfering files form MFP client to FTPServer(our application).
This transfer is done for first scan.
For the second scan it is showing "425 can't open data connection error".
Once the PC is restarted,it is working fine for again for first transfer.
I think the problem may be realated to some socket close.

we are using the followinf comamnds:
USER
PWD
CWD 
TYPE I
PORT
STOR
QUIT.
After STOR command,error is shown.It is unable to create Dataconnection from second scan onwards.

I anyone knows share...it