Microsoft Windows XP service pack 2 comes with inbuilt Firewall. If Microsoft Windows Firewall is blocking a port that is used by a service or by a program, you can configure the Windows Firewall to create an exception. Windows Firewall may be blocking a program or a service if Programs do not respond to a client's request or you do not get data from server.
To open FTP port 21 you need to change Windows Firewall settings.
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