Fatal error when not logged in to WordPress

The plugin works great if logged in to wordpress, but both the calendar page and widgets fail with a fatal error if logged out. Any ideas? Error message follows:

Fatal error: GCE_Display::get_event_days(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "GCE_Event" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /home/content/p3pnexwpnas07_data01/13/2560613/html/wp-content/plugins/google-calendar-events/includes/class-gce-display.php on line 68

https://www.ads-software.com/plugins/google-calendar-events/