Use strict.
And trap for errors:

use strict;
my $ftp = Net::FTP->new( "$G_FTP_SITE" ) or die "Can't connect: $!";
$ftp->login( "$G_FTP_USERNAME","$G_FTP_PASSWORD" ) or die "Can't login
+: $!; 
$ftp->binary () or die "Can't set mode to bin: $!";
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