Fatal error: Uncaught Error: Call to undefined function cal_days_in_month()
in /home/hostdefense/www/wp/wp-content/plugins/backwpup/inc/class-cron.php on line 372

Call stack:

1. BackWPup_Cron::cron_next()
   wp-content/plugins/backwpup/inc/class-install.php:93
2. BackWPup_Install::activate()
   wp-content/plugins/backwpup/backwpup.php:74
3. BackWPup::__construct()
   wp-content/plugins/backwpup/backwpup.php:196
4. BackWPup::get_instance()
   wp-includes/class-wp-hook.php:303
5. WP_Hook::apply_filters()
   wp-includes/class-wp-hook.php:327
6. WP_Hook::do_action()
   wp-includes/plugin.php:470
7. do_action()
   wp-settings.php:441
8. require_once()
   wp-config.php:93
9. require_once()
   wp-load.php:50
10. require_once()
    wp-blog-header.php:13
11. require()
    /home/hostdefense/www/index.php:17