This means that whatever website you're accessing is serving a SSL certificate that is not stored in the certificate store of Perl (see Mozilla::CA).

The two approaches are to either install the appropriate SSL certificate (ask your administrator) and , or to force WWW::Mechanize (and LWP::UserAgent)

Maybe the following works:

 $ua = WWW::Mechanize->new(
      ssl_opts => {
          SSL_ca_path     => '/etc/ssl/file-with-company-certificates'
+,
          verify_hostname => 1,
      }
  );
[download]

The other is to switch off the SSL host verification:

<p>Maybe the following works:</p>
<c>
 $ua = WWW::Mechanize->new(
      ssl_opts => {
          verify_hostname => 0,
      }
  );
[download]