You may also be running afoul of the fact that LWP doesn't handle cookies itself. It's common that you access a login URL, supplying the username and password via POST; the application returns a cookie, which then must be passed back again when GETting a resource.

HTTP::Cookies should help. From the synopsis:

  use HTTP::Cookies;
  $cookie_jar = HTTP::Cookies->new(
    file => "$ENV{'HOME'}/lwp_cookies.dat",
    autosave => 1,
  );

  use LWP;
  my $browser = LWP::UserAgent->new;
  $browser->cookie_jar($cookie_jar);
[download]

At this point, the getting and saving of cookies should happen pretty much automatically.