It seems that the
upgrade method in class-s2-core.php fails to execute the calls to
maybe_add_column, which makes the subscribe2 database table incomplete. This breaks (at least) the public subscription feature.
The visible effect is that a user that tries to subscribe by entering an email address receives a "Sorry, there seems to be an error on the server. Please try again later.".
Is this a compatibility issue with WP 3.5 or do I have an error in my configuration?