Yii连接oracle数据库，报错 [ 新手入门 ]

Yii连接oracle 11g r2数据库，报错。

main.php

'connectionString' =>'oci:dbname=172.30.1.39:1521/orcl',
'username' => 'root',
'password' => 'a'
),

CDbException

CDbConnection 无法开启数据库连线: SQLSTATE[]: pdo_oci_handle_factory: <<Unknown>> (ext\pdo_oci\oci_driver.c:579) 

D:\skill\finance\yii-1.1.10.r3566\framework\db\CDbConnection.php(382)

370                 throw new CDbException(Yii::t('yii','CDbConnection.connectionString cannot be empty.'));
371             try
372             {
373                 Yii::trace('Opening DB connection','system.db.CDbConnection');
374                 $this->_pdo=$this->createPdoInstance();
375                 $this->initConnection($this->_pdo);
376                 $this->_active=true;
377             }
378             catch(PDOException $e)
379             {
380                 if(YII_DEBUG)
381                 {
382                     throw new CDbException(Yii::t('yii','CDbConnection failed to open the DB connection: {error}',
383                         array('{error}'=>$e->getMessage())),(int)$e->getCode(),$e->errorInfo);
384                 }
385                 else
386                 {
387                     Yii::log($e->getMessage(),CLogger::LEVEL_ERROR,'exception.CDbException');
388                     throw new CDbException(Yii::t('yii','CDbConnection failed to open the DB connection.'),(int)$e->getCode(),$e->errorInfo);
389                 }
390             }
391         }
392     }
393 
394     /**
Stack Trace
#0  +– D:\skill\finance\yii-1.1.10.r3566\framework\db\CDbConnection.php(331): CDbConnection->open() 

请问这是什么原因呢？