Removing the cache worked for me.
If you have no access the server from web browser, try using direct URL to purging cache, http://"your-server-address"/admin/purgecaches.php. You will need to login using an admin account. If that does not work or cannot login, use the cli from the server console terminal. Run this command line "sudo -u apache php admin/cli/purge_caches.php" in the Moodle directory.
Hope it helps.