Yii下拉列表不会进行ajax调用

Question

My dropdown menu code:

<?php 
    echo CHtml::dropDownList('symptomCategory', 'symptomCategory',
         $this->getSymptomCategories(),
         array('id'=>'categorySelectDropDown',
               'prompt'=>"Select Symptom Category",  
               'ajax'=> array(
                    'type'=>'POST',
                    'url'=>Yii::app()->createUrl('symptomhistory/updateSymptomsGridView'),
                    'update'=>'#symptoms-grid',
                    'data'=>array('symptomCategory'=>'js:this.value')
               )
         )
    );
?>

My controller action code:

public function actionUpdateSymptomsGridView()
{
    $symptomsModel = new Symptoms;

    if(isset($_POST['symptomCategory']))
    {
        $symptomsModel->setAttributes(array('symptomCategory'=>$_POST['symptomCategory']));
        $dataProvider = $symptomsModel->searchCategory();

        return $dataProvider;
    }
}

I am using firebug to monitor my webapp and it won't fire the ajax calls when I make the change on the dropdownlist. I checked the produced JS code from yii it's this:

jQuery('body').on('change','#categorySelectDropDown',function(){jQuery.ajax({'type':'POST','url':'/mysymptomsbook/index.php?r=symptomhistory/updateSymptomsGridView','data':{'symptomCategory':this.value},'cache':false,'success':function(html){jQuery("#symptoms-grid").html(html)}});return false;});

It should be working but it's not even making any ajax calls. Can someone please help me find what's wrong