This plugin show your google calendar in your weblog wordpress admin pannel.
WARNING! The Uninstall link in Admin Page not have a confirm question, one click and you delete all contributes of Google Calendar Plugin
If you want upgrade from 1.2 to 1.3 version you must uninstall the 1.2 version and going to plugins section, upgrade with wordpress engine the plugin and return to Google Calendar section for use it. If you upgrade without uninstalling the previous version your DB contain one table named: google_calendar_privileges. You must remove that table in manual mode.