Hello, I used LWP::UserAgent to retrieve HTML content of one page and it worked. All of a sudden same code does not work and I get error 503 instead. What might be wrong?

This is the page:
http://www.pubmedcentral.nih.gov/tocrender.fcgi?action=cited&tool=pubmed&pubmedid=17061271

And this is my code: 
    

$pmc_string = "http://www.pubmedcentral.nih.gov/tocrender.fcgi?action=
+cited&tool=pubmed&pubmedid=17061271"; 
 
my $ua = LWP::UserAgent->new; 
$ua->timeout(10); 
$ua->env_proxy; 
 
my $response = $ua->get($pmc_string, 
   'User-Agent' => 'Mozilla/5.0 [en] (Windows; U; Windows NT 6.0)', 
   'Accept' => 'image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, i
+mage/png, */*', 
   'Accept-Charset' => 'iso-8859-1,*,utf-8', 
   'Accept-Language' => 'en-US', 
); 
if ($response->is_success) { 
print $response->content; 
} 
else {die $response->status_line;}

[download]

BTW, LWP::Simple does not work either. Same error 503.

Also, this external website is able to grab their HTML OK; http://web-sniffer.net/?url=http%3A%2F%2Fwww.pubmedcentral.nih.gov%2Ftocrender.fcgi%3Faction%3Dcited%26tool%3Dpubmed%26pubmedid%3D17061271&submit=Submit&http=1.1&rawhtml=yes&type=GET&uak=0

What is wrong with my code? Thanks!

In reply to Getting Error 503 with LWP::UserAgent by mingke

Title:
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and:  <code> code here </code>
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