Anonymous FTP access is only possible on accounts that are IP based (sites that use a unique server IP address).
Most accounts are Name-Based (sharing a common IP address). You have to switch your site to Dedicated IP before proceeding.

 http://www.drundo.info/doc/hsphere/html/configuring_domains.html#switchIP
 
As soon as your domain is available under the new dedicated IP address you can proceed with the anonymous FTP configuration.

 http://www.drundo.info/doc/hsphere/html/ftp.html#anonymous