An HTTP 500 error is a general error message issued by the server when no more specific 5xx message is appropriate.

Correct. But LWP may also generate 500 errors, as a way to communicate fatal errors to the caller:

#!/usr/bin/perl

use 5.010;
use strict;
use warnings;
use LWP::UserAgent;
use Data::Dumper;

my $ua=LWP::UserAgent->new();
my $resp=$ua->get("http://no.such.server.in.my.lan/no-such-page");

say $resp->status_line;
say Dumper $resp;
[download]

500 Can't connect to no.such.server.in.my.lan:80 (Bad hostname)
$VAR1 = bless( {
                 '_content' => 'Can\'t connect to no.such.server.in.my
+.lan:80 (Bad hostname)

LWP::Protocol::http::Socket: Bad hostname \'no.such.server.in.my.lan\'
+ at /usr/lib64/perl5/site_perl/5.12.3/LWP/Protocol/http.pm line 51.
',
                 '_rc' => 500,
                 '_headers' => bless( {
                                        'client-warning' => 'Internal 
+response',
                                        'client-date' => 'Sat, 17 Nov 
+2012 19:32:13 GMT',
                                        'content-type' => 'text/plain'
                                      }, 'HTTP::Headers' ),
                 '_msg' => 'Can\'t connect to no.such.server.in.my.lan
+:80 (Bad hostname)',
                 '_request' => bless( {
                                        '_content' => '',
                                        '_uri' => bless( do{\(my $o = 
+'http://no.such.server.in.my.lan/no-such-page')}, 'URI::http' ),
                                        '_headers' => bless( {
                                                               'user-a
+gent' => 'libwww-perl/6.02'
                                                             }, 'HTTP:
+:Headers' ),
                                        '_method' => 'GET'
                                      }, 'HTTP::Request' )
               }, 'HTTP::Response' );
[download]

Alexander