Program Error (Server Error 500)

<h1>Program Error (Server Error 500)</h1>
                  <hr />
             <p>
              <em>
              More information about this error may be available in the
              server error log and/or program error log.
              </em>
             </p>
             <hr />
               <pre>Base class package &quot;DADA::MailingList::Subscribers::&quot; is empty.
    (Perhaps you need to 'use' the module which defines that package first,
    or make that module available in @INC (@INC contains: ./ ../ ../../ ../../DADA ../../perllib ../../../ ../../../perllib ../../DADA/perllib ./DADA ./DADA/perllib ../../../perl /usr/local/lib/perl5 /usr/local/share/perl5 /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5 /usr/share/perl5 .).
 at /DADA/MailingList/Subscribers.pm line 33
BEGIN failed--compilation aborted at /DADA/MailingList/Subscribers.pm line 33.
Compilation failed in require at /websites/123reg/LinuxPackage24/le/tc/hw/letchworthdtc.org.uk/public_html/cgi-bin/dada/mail.cgi line 191.
BEGIN failed--compilation aborted at /websites/123reg/LinuxPackage24/le/tc/hw/letchworthdtc.org.uk/public_html/cgi-bin/dada/mail.cgi line 191.
</pre>