WP Events Calendar and WordPress upgrade. Deactivate the plug-in as it is NOT compatible with the latest version of WP and will cause your front and back end to disappear. If that happens and you need help, contact me and I can fix the problem for you as each fix I’ve done so far have had different resolutions.
http://wordpress.org/support/topic/411422
http://wordpress.org/support/topic/409138
http://www.wp-eventscalendar.com/
