Warning: Undefined variable $str in /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/init.php on line 71

Fatal error: Uncaught TypeError: Cannot access offset of type string on string in /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-content/plugins/wp-database-backup/includes/admin/class-wpdb-admin.php:2034
Stack trace:
#0 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/class-wp-hook.php(287): WPDB_Admin->wp_db_backup_scheduler_activation(Object(WP))
#1 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters('', Array)
#2 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/plugin.php(544): WP_Hook->do_action(Array)
#3 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/class-wp.php(758): do_action_ref_array('wp', Array)
#4 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-includes/functions.php(1285): WP->main('')
#5 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-blog-header.php(16): wp()
#6 /customers/9/5/1/spiegelhol.nl/httpd.www/blog/index.php(17): require('/customers/9/5/...')
#7 {main}
  thrown in /customers/9/5/1/spiegelhol.nl/httpd.www/blog/wp-content/plugins/wp-database-backup/includes/admin/class-wpdb-admin.php on line 2034