This article provides information about common errors when using FTP with SyncBack V3 freeware or SyncBackSE V4.0.7 and earlier. SyncBackSE V4.0.8 and later, SyncBackPro, SyncBackLite and SyncBackFree, use a different FTP engine and so return less cryptic error messages.


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When testing an FTP connection you may receive one of the following errors:

  • Socket Error # 11001, Host not found: Check that the hostname or IP address has been entered correctly.
  • Socket Error # 11004, Unable to connect: Check to make sure there isn't a trailing or leading space character on the FTP hostname. Also, enter the hostname or IP address, not a URL, e.g. if you have entered something like ftp://my.hostname.com/ then change it to my.hostname.com
  • Socket Error # 10061, Connection refused: The hostname is correct, but either the FTP server is not listening on the port, there is no FTP server running, or a firewall is blocking the connection.
  • Socket Error # 10093: This can happen when the network connection goes down, e.g. the FTP server is no longer connected to the network.
  • Socket Error # 10038: If you are using Serv-U modify your FTP server settings so that the following are unticked: "Block anti time-out schemes", "Block FTP_bounce attacks and FXP", and "Block users who connect more than 6 times within 60 seconds for 30 minutes". You may also want to be sure you are using a passive connection.
  • Socket Error # 10039: There may be a problem getting the IP address for the hostname.
  • Socket Error # 10052: The host you were connected to crashed and rebooted. Try reconnecting at a later time.
  • Unable to connect: Connection time out: The hostname may be incorrect or the FTP server may be behind a firewall.
  • Unable to connect. Not logged in: The username and/or password is not correct.
  • Unable to connect. Error connecting with SSL: The FTP server does not support SSL, or you are using implicit SSL and it only supports explicit, or the wrong port number is being used. If you are using implicit SSL then you probably need to use port 990 instead of port 21.


When running a profile that connects to an FTP server you may receive the following errors in the log file:

  • Scan failed (-1): Read Timeout: The connection to the FTP server was lost, and the attempts to reconnect failed, while trying to scan it for changes.


Other common problems are:

  • Can connect to the FTP server but when trying to choose the destination directory nothing happens for a very long time. Eventually the selection window appears but it's empty: You need to enable Passive mode, or the FTP server is behind a firewall that is not configured correctly


Please note that many routers will intercept FTP commands and change them to try and help with the connection. This is done to pass the correct IP address, for example. Always check that your routers firmware is up-to-date. You may find that using SSL encryption (assuming the FTP server support encryption) can solve problems where the router is "breaking" FTP commands.


If you are using a Dynamic DNS program with your FTP server you may find that disabling passive in the DNS settings (and FTP server) and in SyncBack/SE will fix data transfer problems, i.e. it cannot retrieve a directory listing or files.


In certain firewall configurations, users may encounter Connection Refused errors (#10061) when using SyncBackSE/Pro to establish a connection to a remote site. This is because the firewall is blocking the connection as the permissions for the SyncBackSE/Pro application (within the firewall) are being set to "Trusted Application" instead of "SYSTEM", which will give our application elevated privileges (that our program needs and ask for). It may be necessary to configure the firewall so that it runs the SyncBackSE/Pro application with "SYSTEM" settings:


Allow IP In From Any to Any Where Protocol Is Any


instead of "Trusted Application" settings:


Allow All Incoming and Outgoing Requests


Please note that each firewall configuration is different and the provided setting above is just an example, which may not match your firewall's configuration. Please note that we do not provide bespoke troubleshooting/configuration for firewalls. If required, please consult your firewall administrator or vendor for advice.