我正在使用codeignator，当它在cpanel上正确运行时，但是当我将它托管到plesk时。出现以下错误

我的database.php是

$db['default'] = array(
    'dsn'   => '',
    //'hostname' => '148.66.154.149:3306',
    'hostname' => 'localhost',   
         'dbport' => '3306',
    'username' => 'supergrandgenes',
    'password' => '',
    'database' => 'exam_guide',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => FALSE,
    'db_debug' => TRUE,
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

请帮我解释为什么它不适用于plesk