Can anybody please spot my error, this should be a legal query in SQL shouldn't it??
  Unknown column u.usr_auto_key in the ON clause
This is the database schema:
User: (usr_auto_key, name, etc...)
Setting: (set_auto_key, name etc..)
User_Setting: (usr_auto_key, set_auto_key, value)
And this is the query...
        SELECT 
        `u`.`usr_auto_key` AS `u__usr_auto_key`, 
        `s`.`set_auto_key` AS `s__set_auto_key`, 
        `u2`.`usr_auto_key` AS `u2__usr_auto_key`, 
        `u2`.`set_auto_key` AS `u2__set_auto_key`, 
        `u2`.`value` AS `u2__value` 
        FROM `User` `u`, `Setting` `s` 
        LEFT JOIN `User_Setting` `u2` ON `u`.`usr_auto_key` = `u2`.`usr_auto_key` 
        WHERE (`s`.`sct_auto_key` = 1 AND `u`.`usr_auto_key` = 1 AND admin_property is null)