Some people have experienced issues upgrading to 5.0.0. We will be releasing a 5.0.1 patch sometime next week. If you haven't upgraded yet, we would recommend either waiting for 5.0.1, or replacing the /components/upgrades/tasks/upgrade5_0_0_b1.php file from 5.0.0 with the one attached to this thread.
This attached file will gracefully handle some commonly experienced issues, and the last task, "updateDatabaseCollation" is commented out so that it will not run. When you eventually upgrade to 5.0.1+, you'll be able to update your database collation in Blesta under Tools > Utilities.