Hello druedain,
Please try this:
1. Delete the file uninstall.php from the plugin directory that is currently on the server (found under /wp-content/plugins/all-in-one-event-calendar). Deleting this file ensures that when you uninstall the current version of the plugin, your event data will be preserved when you delete the plugin
2. Deactivate the All-in-One Event Calendar using your WordPress Dashboard.
3. Delete the All-in-One Event Calendar using your WordPress Dashboard.
4. Access your database and go to table wp_option. Sort by field Option_name and delete all the entries that start with “ai1ec”, this will delete plugin settings but events will remain in the database.
5. Install the latest version of the plugin using the WordPress Dashboard.
6. Activate the plugin.