Most browsers submit "anonymous" as your user ID and your email address as your password. The FTP site you are connecting to may not allow "anonymous" access. This error will also occur when the FTP server is currently at its limit of "anonymous" users. Another possibility is that your browser doesn't support anonymous FTP access.
Keep trying to access the FTP site until you succeed. Sometimes the FTP server is too busy. However, if you don't have a browser that allows anonymous FTP access or the site is password-protected, enter your user ID and password manually using FTP software such as WS_FTP or CuteFTP.