bardsart

I just installed Event Calendar and it is the first modification I am making to the site. When I go to the main page I am getting this error message where the calendar should appear: Fatal error: Cannot instantiate non-existent class: calendar in /mnt/w0701/d12/s12/b0289c57/www/theartistatwork.com/catalog/calendar_content.php on line 29 Also: when I go to the admin area and click on event calendar I get a 404 page with the error: The requested URL /index.php was not found on this server. Did I miss something in the install? I'm completely new to OSCommerce and am attempting to understand php as I go along. Any help would be greatly appreciated!