admin-ajax.php problem!

I get this error using admin-ajax.php login…

Warning:  require_once(./wp-includes/registration.php): failed to open stream: No such file or directory in ... /wp-content/plugins/external-db-auth-reloaded/pp_db_auth.phpon line

Fatal error:  require_once(): Failed opening required './wp-includes/registration.php' (include_path='.:/usr/lib/php') in ... /wp-content/plugins/external-db-auth-reloaded/pp_db_auth.php on line 371

Can anyone help me? Thanks 🙂

http://ww.wp.xz.cn/plugins/external-db-auth-reloaded/