ftp site cannot access

This sounds like a firewall\NAT problem.
Does the FTP server have a real world IP address or one from within your domain?
If it's behind a firewall how is the firewall configured? You may need to add a NAT entry for ftp (port 21) to that server's address.

Good luck

You need to do 3 steps

1, Configure your router with static route directing the public ip of your FTP server to the firewall

2, configure your firewall with an object for FTP server. Enable Static NAT using FTP's public IP Address

3, Create another Static route in your firewall for public address of FTP server to it's private address

If you give me specifics on what kind of firewall / Router you use I can give you exact steps