Same with me. As the plugin is from March last year and the last change by my client was in November the error appeared with WP3.3 (or WP3.3.1).
You can reach the events when calling the plugin page. The entry for WP Calendar contains a link to the events page example.de/wp-admin/options-general.php?page=wp-calendar/fsCalendar.php&action=settings
. As the customers usually have no access to the plugin page, the link can still be used by none admins. Customers have to enter the link directly into the browser after login. At the end of the events list is a button to create a new event.
The developer log of this plugin shows, that there has not been any maintenance since the last release date. I’m afraid this plugin is dead.