Your Piwik database is out-of-date, and must be upgraded before you can continue.
Piwik database will be upgraded from version 2.0-rc1 to the new version 2.15.0.
The following dimensions will be updated: log_visit.user_id.
If you have a large Piwik database, updates might take too long to run in the browser. In this situation, you can execute the updates from your command line:
php /var/www/analytics.lamouri.fr/htdocs/console core:update
If you manage a high traffic Piwik server, we recommend to momentarily disable visitor Tracking and put the Piwik User Interface in maintenance mode.
If you are not able to use the command line updater and if Piwik fails to upgrade (due to a timeout of the database, a browser timeout, or any other issue), you could manually execute the SQL queries to update Piwik.
The database upgrade process may take a while, so please be patient.