error on last version 4.9

Let’s assume that the update did not complete, completely.

Try a manual update: https://codex.wordpress.org/Updating_WordPress#Manual_Update

1. This may be a plugin or theme conflict. Please attempt to disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.

See http://www.wpbeginner.com/plugins/how-to-deactivate-all-plugins-when-not-able-to-access-wp-admin/

2. Please install the health check plugin and report back its findings: https://wordpress.org/plugins/health-check/