I have an automated FTP script that is called via Windows Scheduled Tasks every 10 minutes. The script connects to an FTP site to look for a file. If file exists it will pull it to my local. I have noticed that the Winscp command fails with message "Connection Failed" sometimes. Other times it logs on FTP and disconnects just fine. Below is a sample script and error log. At 21:37:02.31 it runs fine. At 21:40:00.20 it fails to connect (no change to script).

::Script
option batch on
option confirm off
open ftp://ftpuser:ftppasswd=@FTPHost
option transfer ascii
lcd C:\ETL\ExcelModelLoads\EntityCashFlows\Asia\Inbox
cd Informatica\EntityCashFlows\Asia
get -delete *.dat
close
exit

::LOG
Process Batch Start - Date: Wed 06/26/2013 Time: 21:37:02.31
. 2013-06-26 21:37:02.846 --------------------------------------------------------------------------
. 2013-06-26 21:37:02.846 WinSCP Version 4.1.7 (Build 413) (OS 6.0.6002 Service Pack 2)
. 2013-06-26 21:37:02.846 Login time: Wednesday, June 26, 2013 9:37:02 PM
. 2013-06-26 21:37:02.846 --------------------------------------------------------------------------
. 2013-06-26 21:37:02.846 Session name: fptuser@FTPHost
. 2013-06-26 21:37:02.846 Host name: FTPHost (Port: 21)
. 2013-06-26 21:37:02.846 User name: fptuser (Password: Yes, Key file: No)
. 2013-06-26 21:37:02.846 Tunnel: No
. 2013-06-26 21:37:02.846 Transfer Protocol: FTP
. 2013-06-26 21:37:02.846 Ping type: C, Ping interval: 30 sec; Timeout: 15 sec
. 2013-06-26 21:37:02.846 Proxy: none
. 2013-06-26 21:37:02.846 FTP: Passive: No
. 2013-06-26 21:37:02.846 Local directory: default, Remote directory: home, Update: No, Cache: Yes
. 2013-06-26 21:37:02.846 Cache directory changes: Yes, Permanent: Yes
. 2013-06-26 21:37:02.846 DST mode: 1
. 2013-06-26 21:37:02.846 --------------------------------------------------------------------------
. 2013-06-26 21:37:02.877 Connecting to FTPHost ...
. 2013-06-26 21:37:02.924 Connected with FTPHost. Waiting for welcome message...
< 2013-06-26 21:37:02.971 220 Microsoft FTP Service
> 2013-06-26 21:37:02.971 USER fptuser
< 2013-06-26 21:37:03.002 331 Password required for fptuser.
> 2013-06-26 21:37:03.002 PASS ********
< 2013-06-26 21:37:03.033 230 User fptuser logged in.
> 2013-06-26 21:37:03.033 SYST
< 2013-06-26 21:37:03.080 215 Windows_NT
> 2013-06-26 21:37:03.080 FEAT
< 2013-06-26 21:37:03.111 211-Extended features supported:
< 2013-06-26 21:37:03.346 SIZE
< 2013-06-26 21:37:03.346 MDTM
< 2013-06-26 21:37:03.346 211 END
. 2013-06-26 21:37:03.346 Connected
. 2013-06-26 21:37:03.346 --------------------------------------------------------------------------
. 2013-06-26 21:37:03.346 Using FTP protocol.
. 2013-06-26 21:37:03.346 Doing startup conversation with host.
> 2013-06-26 21:37:03.346 PWD
< 2013-06-26 21:37:03.393 257 "/" is current directory.
. 2013-06-26 21:37:03.393 Getting current directory name.
. 2013-06-26 21:37:03.393 Startup conversation with host finished.
. 2013-06-26 21:37:03.393 Changing directory to "Informatica\EntityCashFlows\Asia".
> 2013-06-26 21:37:03.393 CWD Informatica\EntityCashFlows\Asia
< 2013-06-26 21:37:03.424 250 CWD command successful.
. 2013-06-26 21:37:03.424 Getting current directory name.
> 2013-06-26 21:37:03.424 PWD
< 2013-06-26 21:37:03.471 257 "/Informatica/EntityCashFlows/Asia" is current directory.
. 2013-06-26 21:37:03.471 Retrieving directory listing...
> 2013-06-26 21:37:03.471 TYPE A
< 2013-06-26 21:37:03.502 200 Type set to A.
> 2013-06-26 21:37:03.518 PORT 10,2,40,114,231,31
< 2013-06-26 21:37:03.549 200 PORT command successful.
> 2013-06-26 21:37:03.549 LIST -a
< 2013-06-26 21:37:03.580 150 Opening ASCII mode data connection for /bin/ls.
< 2013-06-26 21:37:03.814 226 Transfer complete.
. 2013-06-26 21:37:03.814 Directory listing successful
. 2013-06-26 21:37:03.814 Disconnected from server
Process Batch Start - Date: Wed 06/26/2013 Time: 21:40:00.20
. 2013-06-26 21:40:01.459 --------------------------------------------------------------------------
. 2013-06-26 21:40:01.459 WinSCP Version 4.1.7 (Build 413) (OS 6.0.6002 Service Pack 2)
. 2013-06-26 21:40:01.459 Login time: Wednesday, June 26, 2013 9:40:01 PM
. 2013-06-26 21:40:01.459 --------------------------------------------------------------------------
. 2013-06-26 21:40:01.459 Session name: fptuser@FTPHost
. 2013-06-26 21:40:01.459 Host name: FTPHost (Port: 21)
. 2013-06-26 21:40:01.459 User name: fptuser (Password: Yes, Key file: No)
. 2013-06-26 21:40:01.459 Tunnel: No
. 2013-06-26 21:40:01.459 Transfer Protocol: FTP
. 2013-06-26 21:40:01.459 Ping type: C, Ping interval: 30 sec; Timeout: 15 sec
. 2013-06-26 21:40:01.459 Proxy: none
. 2013-06-26 21:40:01.459 FTP: Passive: No
. 2013-06-26 21:40:01.459 Local directory: default, Remote directory: home, Update: No, Cache: Yes
. 2013-06-26 21:40:01.459 Cache directory changes: Yes, Permanent: Yes
. 2013-06-26 21:40:01.459 DST mode: 1
. 2013-06-26 21:40:01.459 --------------------------------------------------------------------------
. 2013-06-26 21:40:01.521 Connection failed.