Error with sql query

Since I installed this plugin the backend of the website has become very slow, in particular no longer able to access wp-admin, but only on approval of users. My database contains many thousands of users and even approve or disable users is impossible. In error_log file admin I found the following errors:

<em>[11-Jun-2015 07:15:50 UTC] WordPress errore sul database Not unique table/alias: 'wp_usermeta' per la query

SELECT SQL_CALC_FOUND_ROWS wp_users.* FROM wp_users INNER JOIN wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) INNER JOIN wp_usermeta wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) WHERE 1=1 AND (
( wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘pending’ )
) AND ( (wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘pending’) ) ORDER BY user_login ASC` fatta da require_once(‘wp-admin/admin.php’), require(‘wp-admin/menu.php’), require_once(‘wp-admin/includes/menu.php’), do_action(‘admin_menu’), call_user_func_array, pw_new_user_approve_user_list->pending_users_bubble, pw_new_user_approve->get_user_statuses, pw_new_user_approve->_get_user_statuses, WP_User_Query->__construct, WP_User_Query->query
[11-Jun-2015 07:15:50 UTC] WordPress errore sul database Not unique table/alias: <strong>’wp_usermeta’ per la query SELECT DISTINCT SQL_CALC_FOUND_ROWS wp_users.* FROM wp_users LEFT JOIN wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) LEFT JOIN wp_usermeta AS mt1 ON (wp_users.ID = mt1.user_id AND mt1.meta_key = ‘pw_user_status’ ) INNER JOIN wp_usermeta wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) WHERE 1=1 AND (
( wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘approved’ )
OR
mt1.user_id IS NULL
) AND ( (wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘pending’) ) ORDER BY user_login ASC</strong> fatta da require_once(‘wp-admin/admin.php’), require(‘wp-admin/menu.php’), require_once(‘wp-admin/includes/menu.php’), do_action(‘admin_menu’), call_user_func_array, pw_new_user_approve_user_list->pending_users_bubble, pw_new_user_approve->get_user_statuses, pw_new_user_approve->_get_user_statuses, WP_User_Query->__construct, WP_User_Query->query
[11-Jun-2015 07:15:50 UTC] WordPress errore sul database Not unique table/alias: <strong>’wp_usermeta’ per la query SELECT SQL_CALC_FOUND_ROWS wp_users.* FROM wp_users INNER JOIN wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) INNER JOIN wp_usermeta wp_usermeta ON ( wp_users.ID = wp_usermeta.user_id ) WHERE 1=1 AND (
( wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘denied’ )
) AND ( (wp_usermeta.meta_key = ‘pw_user_status’ AND CAST(wp_usermeta.meta_value AS CHAR) = ‘pending’) ) ORDER BY user_login ASC </strong> fatta da require_once(‘wp-admin/admin.php’), require(‘wp-admin/menu.php’), require_once(‘wp-admin/includes/menu.php’), do_action(‘admin_menu’), call_user_func_array, pw_new_user_approve_user_list->pending_users_bubble, pw_new_user_approve->get_user_statuses, pw_new_user_approve->_get_user_statuses, WP_User_Query->__construct, WP_User_Query->query</em>
`
I can not figure out how to make the plugin to generate these queries that require 2 user status simultaneously

https://ww.wp.xz.cn/plugins/new-user-approve/