You should check the return codes after each call to a Net::FTP method (actually, the code I present below should work for just about any Net:: module that comes with libnet, not just Net::FTP). See the below code:

use Net::FTP;
$ftp = Net::FTP->new("www.somedomain.org");
check_net_err($ftp);
$ftp->login("user","password");
check_net_err($ftp);
$ftp->cwd("/pages");
check_net_err($ftp);
$ftp->get("defhome.htm");
check_net_err($ftp);
$ftp->quit;


sub check_net_err{
  my $net=shift;
  if(!defined $net){
    die "Net:: object not defined $!";
  }else{
    if((!$net->ok())||($net->code() >= 400)){
      die "Net:: error ".$net->code()." : ".$net->message();
    }
  }
}
[download]

You can set the Debug flag on the Net::FTP->new call and get a trace of the session dumped to STDERR.

my $ftp = Net::FTP->new("www.somedomain.org",Debug=>1);
[download]

example output of Net::FTP w/ Debug=>1

Net::FTP: Net::FTP(2.40)
Net::FTP:   Exporter
Net::FTP:   Net::Cmd(2.12)
Net::FTP:   IO::Socket::INET(1.24)
Net::FTP:     IO::Socket(1.25)
Net::FTP:       IO::Handle(1.21)

Net::FTP=GLOB(0x81f20e4)<<< 220 www.somedomain.org FTP server (Version wu-2.6.0(1) Thu Oct 21 12:27:00 EDT 1999) ready.
Net::FTP=GLOB(0x81f20e4)>>> user someusername
Net::FTP=GLOB(0x81f20e4)<<< 331 Password required for someusername.
Net::FTP=GLOB(0x81f20e4)>>> PASS ........
Net::FTP=GLOB(0x81f20e4)<<< 230 User someusername logged in.
Net::FTP=GLOB(0x81f20e4)>>> CWD /pages
Net::FTP=GLOB(0x81f20e4)<<< 550 /pages: No such file or directory.
Net:: error 550 : /pages: No such file or directory.
Net::FTP=GLOB(0x81f20e4)>>> QUIT
Net::FTP=GLOB(0x81f20e4)<<< 221-You have transferred 0 bytes in 0 files.
Net::FTP=GLOB(0x81f20e4)<<< 221-Total traffic for this session was 269 bytes in 0 transfers.
Net::FTP=GLOB(0x81f20e4)<<< 221-Thank you for using the FTP service on www.somedomain.org.
Net::FTP=GLOB(0x81f20e4)<<< 221 Goodbye.

You may want to check out the earlier post Trapping errors from NET::Ftp for some other approaches.