Alias "ext.backtotop.backtotop" Is Invalid. Make Sure It Points To An Existing Php File And The File Is Readable.

hi i'm newer on yii when i attach theme for my fresh application .i edit config.php like this

'theme'=>'theme_name',

i done this several time but now if i do this it display like this error


CException

Alias "ext.backToTop.BackToTop" is invalid. Make sure it points to an existing PHP file and the file is readable.

E:\wamp\yii\framework\YiiBase.php(318)

306 if($isClass && (class_exists($className,false) || interface_exists($className,false)))
307 return self::$_imports[$alias]=$className;
308
309 if(($path=self::getPathOfAlias($alias))!==false)
310 {
311 if($isClass)
312 {
313 if($forceInclude)
314 {
315 if(is_file($path.'.php'))
316 require($path.'.php');
317 else
318 throw new CException(Yii::t('yii','Alias "{alias}" is invalid. Make sure it points to an existing PHP file and the file is readable.',array('{alias}'=>$alias)));
319 self::$_imports[$alias]=$className;
320 }
321 else
322 self::$classMap[$className]=$path.'.php';
323 return $className;
324 }
325 else // a directory
326 {
327 if(self::$_includePaths===null)
328 {
329 self::$_includePaths=array_unique(explode(PATH_SEPARATOR,get_include_path()));
330 if(($pos=array_search('.',self::$_includePaths,true))!==false)

Stack Trace
#0
+
E:\wamp\yii\framework\web\CWidgetFactory.php(147): YiiBase::import("ext.backToTop.BackToTop", true)
#1
+
E:\wamp\yii\framework\web\CBaseController.php(147): CWidgetFactory->createWidget(RegistrationController, "ext.backToTop.BackToTop", array("text" => "Back To Top", "autoShow" => true))
#2
+
E:\wamp\yii\framework\web\CBaseController.php(173): CBaseController->createWidget("ext.backToTop.BackToTop", array("text" => "Back To Top", "autoShow" => true))
#3
–
E:\wamp\www\theGuider\themes\bizapps\views\layouts\main.php(51): CBaseController->widget("ext.backToTop.BackToTop", array("text" => "Back To Top", "autoShow" => true))

46
47 &lt!--back to tp extention -->
48 <?php $this->widget('ext.backToTop.BackToTop',array(
49 'text'=>'Back To Top',
50 'autoShow'=>true
51 ));?>
52 &lt!-- /.nav -->
53
54
55 &lt!-- .download button -->
56

#4
+
E:\wamp\yii\framework\web\CBaseController.php(127): require("E:\wamp\www\theGuider\themes\bizapps\views\layouts\main.php")
#5
+
E:\wamp\yii\framework\web\CBaseController.php(96): CBaseController->renderInternal("E:\wamp\www\theGuider\themes\bizapps\views//layouts/main.php", array("content" => "<div id="content"> <h1>Registration</h1> <div class="for..."), true)
#6
+
E:\wamp\yii\framework\web\widgets\CContentDecorator.php(77): CBaseController->renderFile("E:\wamp\www\theGuider\themes\bizapps\views//layouts/main.php", array("content" => "<div id="content"> <h1>Registration</h1> <div class="for..."), true)
#7
+
E:\wamp\yii\framework\web\widgets\CContentDecorator.php(55): CContentDecorator->decorate("<div id="content"> <h1>Registration</h1> <div class="for...")
#8
+
E:\wamp\yii\framework\web\widgets\COutputProcessor.php(45): CContentDecorator->processOutput("<div id="content"> <h1>Registration</h1> <div class="for...")
#9
+
E:\wamp\yii\framework\web\CBaseController.php(207): COutputProcessor->run()
#10
+
E:\wamp\yii\framework\web\CBaseController.php(301): CBaseController->endWidget("CContentDecorator")
#11
–
E:\wamp\www\theGuider\protected\views\layouts\column1.php(6): CBaseController->endContent()

1 <?php /* @var $this Controller */ ?>
2 <?php $this->beginContent('//layouts/main'); ?>
3 <div id="content">
4 <?php echo $content; ?>
5 </div>&lt!-- content -->
6 <?php $this->endContent(); ?>

#12
+
E:\wamp\yii\framework\web\CBaseController.php(127): require("E:\wamp\www\theGuider\protected\views\layouts\column1.php")
#13
+
E:\wamp\yii\framework\web\CBaseController.php(96): CBaseController->renderInternal("E:\wamp\www\theGuider\protected\views//layouts/column1.php", array("content" => " <h1>Registration</h1> <div class="form"> <form enctype="..."), true)
#14
+
E:\wamp\yii\framework\web\CController.php(785): CBaseController->renderFile("E:\wamp\www\theGuider\protected\views//layouts/column1.php", array("content" => " <h1>Registration</h1> <div class="form"> <form enctype="..."), true)
#15
–
E:\wamp\www\theGuider\protected\modules\user\controllers\RegistrationController.php(81): CController->render("/user/registration", array("model" => RegistrationForm, "profile" => Profile))

76 $this->refresh();
77 }
78 }
79 } else $profile->validate();
80 }
81 $this->render('/user/registration',array('model'=>$model,'profile'=>$profile));
82 }
83 }
84 }

#16
+
E:\wamp\yii\framework\web\actions\CInlineAction.php(50): RegistrationController->actionRegistration()
#17
+
E:\wamp\yii\framework\web\CController.php(309): CInlineAction->runWithParams(array("r" => "user/registration"))
#18
+
E:\wamp\yii\framework\web\CController.php(287): CController->runAction(CInlineAction)
#19
+
E:\wamp\yii\framework\web\CController.php(266): CController->runActionWithFilters(CInlineAction, array())
#20
+
E:\wamp\yii\framework\web\CWebApplication.php(283): CController->run("")
#21
+
E:\wamp\yii\framework\web\CWebApplication.php(142): CWebApplication->runController("user/registration")
#22
+
E:\wamp\yii\framework\base\CApplication.php(162): CWebApplication->processRequest()
#23
+
E:\wamp\www\theGuider\index.php(13): CApplication->run()
2013-04-04 09:57:11 Apache/2.2.22 (Win32) PHP/5.3.13 Yii Framework/1.1.12



please give me a solution ....