Something to consider: some web servers are "agent sensitive". Check out this doco:

             $ua->agent('Checkbot/0.4 ' . $ua->_agent);
             $ua->agent('Checkbot/0.4 ');    # same as above
             $ua->agent('Mozilla/5.0');
             $ua->agent("");                 # don't identify
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I'd pick something benign like 'Mozilla/5.0' to set your agent's ID to and you may have more success. I've run into this issue a few times...