The WordPress dashboard is filled with Warnings and errors

When I installed and activated the plugin my dashboard is filled with warnings and errors:

Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /var/www/blog1/wp-includes/functions.php on line 3006

Notice: Undefined index: common in /var/www/blog1/wp-content/plugins/ready-backup/classes/errors.php on line 83

Notice: Undefined index: jquery in /var/www/blog1/wp-content/plugins/ready-backup/classes/frame.php on line 308

When I clicked on “Start using Plugin”, it just got stuck.