auditTrail yii extension - php

Question

I am a newbie to yii and I am installing extension auditTrail.
I have made all the required changes to my main.php config file but everytime it is showing the same error
'Alias "auditTrail.AuditTrailModule" is invalid. Make sure it points
to an existing PHP file and the file is readable.'
Please help me out. thankyou in advance.. my editted file is here:
// uncomment the following to define a path alias
// Yii::setPathOfAlias('local','path/to/local-folder');
// This is the main Web application configuration. Any writable
// CWebApplication properties can be configured here.
return array(
'basePath'=>dirname(__FILE__).DIRECTORY_SEPARATOR.'..',
'name'=>'My Web Application',
// preloading 'log' component
'preload'=>array('log'),
// autoloading model and component classes
'import'=>array(
'application.models.*',
'application.components.*',
'application.modules.auditTrail.models.AuditTrail',
),
'modules'=>array(
'auditTrail'=>array(),
// uncomment the following to enable the Gii tool
'gii'=>array(
'class'=>'system.gii.GiiModule',
'password'=>false,
// If removed, Gii defaults to localhost only. Edit carefully to taste.
'ipFilters'=>array('127.0.0.1','::1'),
),
),
// application components
'components'=>array(
'user'=>array(
// enable cookie-based authentication
'allowAutoLogin'=>true,
),
// uncomment the following to enable URLs in path-format
'urlManager'=>array(
'urlFormat'=>'path',
'rules'=>array(
'<controller:\w+>/<id:\d+>'=>'<controller>/view',
'<controller:\w+>/<action:\w+>/<id:\d+>'=>'<controller>/<action>',
'<controller:\w+>/<action:\w+>'=>'<controller>/<action>',
),
),
'db'=>array(
'connectionString' => 'sqlite:'.dirname(__FILE__).'/../data/testdrive.db',
),
// uncomment the following to use a MySQL database
'db'=>array(
'connectionString' => 'mysql:host=localhost;dbname=assetdb',
'emulatePrepare' => true,
'username' => 'root',
'password' => 'Preksha#12',
'charset' => 'utf8',
),
'errorHandler'=>array(
// use 'site/error' action to display errors
'errorAction'=>'site/error',
),
'log'=>array(
'class'=>'CLogRouter',
'routes'=>array(
array(
'class'=>'CFileLogRoute',
'levels'=>'error, warning',
),
// uncomment the following to show log messages on web pages
/*
array(
'class'=>'CWebLogRoute',
),
*/
),
),
),
// application-level parameters that can be accessed
// using Yii::app()->params['paramName']
'params'=>array(
// this is used in contact page
'adminEmail'=>'webmaster#example.com',
),
);
here is the error ::
CException
Alias "auditTrail.AuditTrailModule" is invalid. Make sure it points to an existing PHP file and the file is readable.