internal server Error when load ajax in yii - php

Question

I had problem in loading Ajax , I knew that by got screanshot of request by
Tamper Data :
http://up.arabseyes.com/uploads/02_12_1213544389861.jpg
result was : internal server Error .
What is the problem in my code ?
View :
<?php
/* #var $this UsersController */
/* #var $model Users */
/* #var $form CActiveForm */
?>
<div class="form">
<?php $form=$this->beginWidget('CActiveForm', array(
'id'=>'users-index-form',
'enableAjaxValidation'=>false,
)); ?>
<?php echo $form->errorSummary($model); ?>
<div class="row">
<?php echo $form->labelEx($model,'الأسم الأول'); ?>
<?php echo $form->textField($model,'first_name'); ?>
<?php echo $form->error($model,'الأسم الاول'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'العائلة'); ?>
<?php echo $form->textField($model,'last_name'); ?>
<?php echo $form->error($model,'العائلة'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'كلمة المرور'); ?>
<?php echo $form->passwordField($model,'password'); ?>
<?php echo $form->error($model,'password'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'تأكيد كلمة المرور'); ?>
<?php echo $form->passwordField($model,'passwordconfirm'); ?>
<?php echo $form->error($model,'passwordconfirm'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'البريد الإلكتروني '); ?>
<?php echo $form->textField($model,'email'); ?>
<?php echo $form->error($model,'email'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'تأكيد البريد الإلكتروني'); ?>
<?php echo $form->textField($model,'emailconfirm'); ?>
<?php echo $form->error($model,'emailconfirm'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'تاريخ الميلاد'); ?>
<?php
$this->widget(
'ext.jui.EJuiDateTimePicker',
array(
'model' => $model,
'attribute' => 'birth_date',
'language'=> 'en',//default Yii::app()->language
'mode' => 'date',//'datetime' or 'time' ('datetime' default)
'options' => array(
'dateFormat' => 'yy-mm-dd',
//'timeFormat' => '',//'hh:mm tt' default
),
)
);
?>
<?php echo $form->error($model,'birth_date'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'الجنس'); ?>
<?php echo chtml::activeDropDownList($model,'gender',$model->getStatusOption(),array('prompt'=>'أختر جنسك')
); ?>
<?php echo $form->error($model,'gender'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'البلد'); ?>
<?php
/*
echo chtml::activeDropDownList($model,'country',$model->getcountry(),array('prompt'=>'اختر بلدك ') ,
array(
'ajax' => array(
'type'=>'POST', //request type
'url'=>CController::createUrl('current/dynamiccities'), //url to call.
//Style: CController::createUrl('currentController/methodToCall')
'update'=>'#city', //selector to update
//'data'=>'js:javascript statement'
//leave out the data key to pass all form values through
))
);
*/
echo CHtml::activedropDownList($model,'country',$model->getcountry(),
array(
'ajax' => array(
'type'=>'POST', //request type
'url'=>CController::createUrl('Register/dynamiccities'), //url to call.
//Style: CController::createUrl('currentController/methodToCall')
'update'=>'#city', //selector to update
//'data'=>'js:javascript statement'
//leave out the data key to pass all form values through
))
);
?>
<?php echo $form->error($model,'country'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'المدينة'); ?>
<?php
//empty since it will be filled by the other dropdown
echo CHtml::dropDownList('city','', array());
?>
<?php echo $form->error($model,'city'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'رمز الاتصال'); ?>
<?php echo $form->textField($model,'mobile_code'); ?>
<?php echo $form->error($model,'mobile_code'); ?>
</div>
<div class="row">
<?php echo $form->labelEx($model,'رقم الجوال'); ?>
<?php echo $form->textField($model,'mobile_number'); ?>
<?php echo $form->error($model,'mobile_number'); ?>
</div>
<div class="row buttons">
<?php echo CHtml::submitButton('تسجيــــــــــــل'); ?>
</div>
<?php $this->endWidget(); ?>
</div><!-- form -->
Controller :
....
public function actionDynamiccities() /// call Ajax
{
$data=Cities::model()->findAll('country=:country_id',
array(':country_id'=>(int) $_POST['country']));
$data=CHtml::listData($data,'id','city_name_e');
foreach($data as $value=>$name)
{
echo CHtml::tag('option',
array('value'=>$value),CHtml::encode($name),true);
};
}
....
Thanks in Advance .