Try setting UserAgent to same as your browser

#!perl
use strict;
use warnings;
use LWP::UserAgent();
printf "%s Perl %s LWP %s\n\n",$^O,$^V,$LWP::VERSION; 

my $url= 'http://server_address:port/ws/1/console/webstart?full=true';
my $ua = LWP::UserAgent->new;
$ua->agent("Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)");
my $resp = $ua->head($url);

print $resp->as_string;
[download]

What is the size in bytes of the file downloaded via the browser ?