Geting the following error. What can be the cause?

500 Can't locate HTML/HeadParser.pm in @INC (@INC contains: /usr/lib/perl5/5.00503/i386-linux /usr/lib/perl5/5.00503 /usr/lib/perl5/site_perl/5.005/i386-linux /usr/lib/perl5/site_perl/5.005 .)
Attempted retrieval URL: http://dmoz.org