After restarting ftp server found that the ftp server is not running, Checked the system log of the server & found the following error.
pure-ftpd: (?@?) [ERROR] Unable to start a standalone server: [Invalid argument]
In debian etch 4, The pure-ftpd-mysql does not have link to pure-ftpd from pure-ftpd-mysql by default. Apply the link by force and restart the service.
ln -sf /usr/sbin/pure-ftpd-mysql /usr/sbin/pure-ftpd