[otrs] how to add a module?

I tried to add a module in otrs: AdminCustomerGroup.pm The module is located at : /opt/otrs/Kernel/Modules it is referenced by: AdminNavigationBar.dtl It is also added in /opt/otrs/scripts/apache2-perl-startup.pl However, when I click the button on the navigation bar, I am getting [ http://helpdesk.monterey.k12.ca.us/otrs//otrs/index.pl?OTRS ] Alex Zheng (azheng@monterey.k12.ca.us) Fri Dec 19 08:16:12 2003 Error: Action 'AdminCustomerGroup' not found! Comment: Perhaps the admin forgot to load "Kernel::Modules::AdminCustomerGroup"! what else do I need to do? thanks. alex