Generally, this page is there to let you know when we've updated the database schema so you can make appropriate changes. Be sure to run rb-site upgrade /path/to/site. See Upgrading Sites for more information on this.

If you've done that already and you're still getting the error, and you're using sqlite for your database, you may need to set DATABASE_NAME in your site's file to the absolute path of the database instead of the relative path. See this thread for more information.