Yii Radiobuttonlist即使被选中也显示'不能为空'

I am working with ajax crud in Yii. I have a radiobuttonlist in the form. I get 'cannot be blank' error even if it is selected. Please help me find the problem.

In the ajax_form the code is:

$form=$this->beginWidget('CActiveForm', array(
 'id'=>'universal-electives-form',
//  'htmlOptions' => array('enctype' => 'multipart/form-data'),
     'action' => $actionUrl,
// 'enableAjaxValidation'=>true,
  'enableClientValidation'=>true,
 'focus'=>array($model,'name'),
 'errorMessageCssClass' => 'input-notification-error  error-simple png_bg',
 'clientOptions'=>array('validateOnSubmit'=>true,
                                    'validateOnType'=>false,
                                    'afterValidate'=>'js_afterValidate',
                                    'errorCssClass' => 'err',
                                    'successCssClass' => 'suc',
                                    'afterValidate' => 'js:function(form,data,hasError){ $.js_afterValidate(form,data,hasError);  }',
                                     'errorCssClass' => 'err',
                                    'successCssClass' => 'suc',
                                    'afterValidateAttribute' => 'js:function(form, attribute, data, hasError){
                                                                                             $.js_afterValidateAttribute(form, attribute, data, hasError);
                                                                                                                        }'
                                                                         ),

));

 <?php echo $form->labelEx($model,'offered_for',array('style'=>'color:#000000')); ?>
 <?php echo $form->radioButtonList($model,'offered_for',array('1'=>'Boys','2'=>'Girls','0'=>'Both')); ?>
 <?php echo $form->error($model,'offered_for'); ?>

In the model, the rules are:

public function rules()
{
    // NOTE: you should only define rules for those attributes that
    // will receive user inputs.
    return array(
        array('name, desc, batch, offered_for, created_by, created_at', 'required'),
        array('offered_for, created_by', 'numerical', 'integerOnly'=>true),
        array('name, desc, batch', 'length', 'max'=>255),
        // The following rule is used by search().
        // Please remove those attributes that should not be searched.
        array('id, name, desc, batch, offered_for, created_by, created_at', 'safe', 'on'=>'search'),
    );
}

In the controller:

public function actionAjax_Create(){
    if(isset($_POST['UniversalElectives']))
    {
        $model=new UniversalElectives;
        $batch_ids = '';
        $count = count($_POST['UniversalElectives']['batch']);          
        //set the submitted values
        $model->attributes=$_POST['UniversalElectives'];
        $model->offered_for = $POST['UniversalElectives']['offered_for'];
        for($i=0;$i<=$count;$i++)
        {
            if($i!=0 and $i!=$count){
                $batch_ids = $batch_ids.',';
            }
            $batch_ids = $batch_ids.$_POST['UniversalElectives']['batch'][$i];
        }
        $model->batch = $batch_ids;
        $model->created_by = Yii::app()->user->id;
        $model->created_at = date('Y-m-d h:i:s');
        //return the JSON result to provide feedback.
        if($model->save(false)){
            echo json_encode(array('success'=>true,'id'=>$model->primaryKey) );
            exit;
        } else
        {
            echo json_encode(array('success'=>false));
            exit;
        }
    }
}