Please see what you have put in the Address field. You will need the valid hostname of an ftp server or a valid IP address.
If connecting through the favorites. Only the name or address of the FTP server belongs in the host section. You should not include URL or path information in this field.
If you have verified that the hostname is correct, there may be a problem with your DNS server (or with your ISP's DNS server if you are a standalone user). It may be unable to resolve hostnames to IP addresses.