I would start with the debugging script found in libnet FAQ:

#!/your/path/to/perl


use Net::FTP;


my $ftp = new Net::FTP ($host, DEBUG=> 1);
$ftp->login('user', 'password');
$ftp->quit;
[download]

Next, I agree with derby that you need to get into passive mode. Using Net::Config, there are a couple ways of doing that. One, if you are behind a firewall, then set ftp_ext_passive to a true value. Second, if you're not behind a firewall, you can set ftp_int_passive to a true value. There's one more method. If you're behind a FTP proxy firewall, not an HTTP or SOCKS firewall, then ftp_firewall must be set to "hostname:port"(the port that the firewall listens to).