I updated your module with overwrite of the 2.7 files but then Drupal gives in all sections an Error 500. If i remove your module it works all again. I tried to run the update.php of Drupal it gives me some errors. If i go back to version 2.7 it has the same effect. I refreshed also the Drupal cache.
I have following error messages since Mailchimp 2.8:
Recoverable fatal error: Argument 2 passed to SelectQuery::fields() must be an array, null given, called in /var/www/vhosts/neofelis/includes/entity.inc on line 284 and defined in SelectQuery->fields() (Line 1300 from /var/www/vhosts/neofelis/includes/database/select.inc).