jos-Error: Unable to load renderer class

JSite -> dispatch() @ /home/musicedm/public_html/index.php:42
JComponentHelper :: renderComponent() @ /home/musicedm/public_html/includes/application.php:194
JError :: raiseError() @ /home/musicedm/public_html/libraries/joomla/application/component/helper.php:335
JError :: raise() @ /home/musicedm/public_html/libraries/joomla/error/error.php:251
JError :: throwError() @ /home/musicedm/public_html/libraries/joomla/error/error.php:176
call_user_func_array() @ /home/musicedm/public_html/libraries/joomla/error/error.php:214
JError :: handleCallback()
call_user_func() @ /home/musicedm/public_html/libraries/joomla/error/error.php:765
JError :: customErrorPage()
JDocumentError -> render() @ /home/musicedm/public_html/libraries/joomla/error/error.php:804
JDocumentError -> _loadTemplate() @ /home/musicedm/public_html/libraries/joomla/document/error/error.php:107
require_once() @ /home/musicedm/public_html/libraries/joomla/document/error/error.php:135
Gantry -> displayModules() @ /home/musicedm/public_html/templates/rt_metropolis/error.php:45
GantryModulesRenderer :: display() @ /home/musicedm/public_html/libraries/gantry/core/gantry.class.php:867
GantryFeatureDropdownMenu -> render() @ /home/musicedm/public_html/libraries/gantry/core/renderers/gantrymodulesrenderer.class.php:65
JDocument -> loadRenderer() @ /home/musicedm/public_html/templates/rt_metropolis/features/dropdownmenu.php:50
JError :: raiseError() @ /home/musicedm/public_html/libraries/joomla/document/document.php:926
JError :: raise() @ /home/musicedm/public_html/libraries/joomla/error/error.php:251