Set it up. Updated settings.
Page created ("Calendar").
But I was still getting the error message "Settings not updated". So I went into settings and selected the same settings as before, and clicked on UPDATE SETTINGS.
This led to http 500 error. I couldn't see even the dashboard.
So I had to manually delete the "all-in-one.." folder.
When i reinstall the plugin, I see this error:
Fatal error: Ai1ec_Settings::get_instance() [<a href='ai1ec-settings.get-instance'>ai1ec-settings.get-instance</a>]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Ai1ec_Settings" 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/mydomain/public_html/wordpress/wp-content/plugins/all-in-one-event-calendar/app/model/class-ai1ec-settings.php on line 242