SFTP closing connection

Hi,

I am trying to use the following script to run a batch SFTP using WinSCP3. I am trying to FTP 2 files, each file is of size 500 MB. I started the script overnight and today i see that FTP has failed for reason "Host has not answered for 15 seconds." Given below is the script i tried to use and the Error logs; Could you pls help?
Thanks in advance

Script
-----

option batch on
option confirm off
open username@<IP address>
cd dropzone
transfer binary
lcd G:\sftp\testfolder
put test1.csv.aa.gz
put test2.csv.ab.gz
close
exit

Logs
----
batch on
confirm off
Initialisation...
Searching for host...
Connecting to host...
Authenticating...
Using username "username".
'username@IP Address' session password:
Authenticated.
Starting the session...
Reading remote directory...
Session started.
Active session: [1] username@IP
/
Unknown command 'transfer'.
G:\sftp\testfolder
test1.csv.aa | 244084 kB | 67.8 kB/s | binary | 56%
Authenticating...
test1.csv.aa | 244112 kB | 67.8 kB/s | binary | 56%
Host has not answered for 15 seconds.
Wait for another 15 seconds? Pressing 'Abort' button will close session.
(A)bort, (R)etry: Abort
test1.csv.aa | 244124 kB | 67.5 kB/s | binary | 56%
Copying files to remote side failed.
Terminated by user.
Session 'username@IP' closed.

Does the error repeat? If it has happend only once, I can hardly give you any hint. The connection to your server can have been simply lost in the middle of the transfer. It happens. If the error repeats come back and post a log file.