MODX - 500 Error - Site temporarily unavailable

Ошибка:

500 Error - Site temporarily unavailable

сразу смотрим логи по адресу core/cache/logs/error.log

Одна из возможны причин и ошибок - неверный конфиг для подключения к mysql:

[2016-01-17 14:03:06] (ERROR in xPDOConnection::connect @ /home/admin/web/site.com/public_html/core/xpdo/xpdo.class.php : 3046) SQLSTATE[28000] [1045] Access denied for user 'admin_100'@'localhost' (using password: YES)
[2016-01-17 14:03:06] (ERROR in xPDOConnection::connect @ /home/admin/web/site.com/public_html/core/xpdo/xpdo.class.php : 3046) SQLSTATE[28000] [1045] Access denied for user 'admin_100'@'localhost' (using password: YES)
[2016-01-17 14:03:06] (ERROR @ /index.php) Error preparing statement for query: SELECT `modSystemSetting`.`key` AS `modSystemSetting_key`, `modSystemSetting`.`value` AS `modSystemSetting_value`, `modSystemSetting`.`xtype` AS `modSystemSetting_xtype`, `modSystemSetting`.`namespace` AS `modSystemSetting_namespace`, `modSystemSetting`.`area` AS `modSystemSetting_area`, `modSystemSetting`.`editedon` AS `modSystemSetting_editedon` FROM `modx_system_settings` AS `modSystemSetting`  -
[2016-01-17 14:03:06] (ERROR in xPDOConnection::connect @ /home/admin/web/site.com/public_html/core/xpdo/xpdo.class.php : 3046) SQLSTATE[28000] [1045] Access denied for user 'admin_100'@'localhost' (using password: YES)
[2016-01-17 14:03:06] (ERROR in xPDOConnection::connect @ /home/admin/web/site.com/public_html/core/xpdo/xpdo.class.php : 3046) SQLSTATE[28000] [1045] Access denied for user 'admin_100'@'localhost' (using password: YES)
[2016-01-17 14:03:06] (ERROR @ /index.php) Error preparing statement for query: SELECT `modSystemSetting`.`key` AS `modSystemSetting_key`, `modSystemSetting`.`value` AS `modSystemSetting_value`, `modSystemSetting`.`xtype` AS `modSystemSetting_xtype`, `modSystemSetting`.`namespace` AS `modSystemSetting_namespace`, `modSystemSetting`.`area` AS `modSystemSetting_area`, `modSystemSetting`.`editedon` AS `modSystemSetting_editedon` FROM `modx_system_settings` AS `modSystemSetting`  -
[2016-01-17 14:03:06] (FATAL) Could not load core MODX configuration!

Решение - исправить данные для подключения к базе в конфиг файле MODX - core/config/config.inc.php