Sudden problems with LWP::UserAgent

[cross post from perlmonks]
Hi,

I guess this is more a question of how to get around a website
blocking LWP::UserAgent. I have been using this code for a while now

#!/usr/bin/perl -w

use diagnostics;
use strict;
use LWP;
use Date::Manip;
use HTTP::Cookies;
use URI;

my $cookie_jar;
$cookie_jar = HTTP::Cookies->new(
    'file'  =>  'cookies.lwp',
    'autosave'  => 1,
);
my $url = URI->new
('http://www.nseindia.com/marketinfo/indices/indexwatch.jsp');

my $browser = LWP::UserAgent->new(timeout=>'45',
agent=>'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.11)
Gecko/20101012 Firefox/3.6.11');
$browser->cookie_jar($cookie_jar);
push @{ $browser->requests_redirectable }, 'POST';

my $html_page;

my $response = $browser->get($url);
if ($response->is_error()) {
    print "error in getting index ".$response->status_line()."\n";
    print "try again...\n";
} else {
    $html_page = $response->content();
    if ($html_page =~ m{<a href=#top>Top</a></center>}) {
        print "got Index\n";
    } elsif ($html_page =~ m/Your request could not be processed/) {
        print "\t\t\tNSE is down. Try again...\n\n";
    } else {
        print "$html_page\n";
        print "failed to get index. Try again...\n";
    }
}

This code worked till yesterday. However today I am hitting the 403 error.
"
error in getting index 403 Forbidden
try again...
"

I used the same UserAgent as that of Mozilla which successfully
retrieves the page. I tried it from different IP address to ensure
that my IP is not blocked(I run it once a day and am not running a
bot) Looking for some help in getting this going again.

Thanks Uday