datePickerGroup and NAN value

Hello i am new in Yii, i generate bootstrap crud and it work fine when i create a form, i use

<?php echo $form->datePickerGroup($model,‘date’,array(‘widgetOptions’=>array(‘options’=>‘format’=>‘dd/mm/yyyy’)), ‘prepend’=>’’);

this work good but when i want to modify the date i have NAN error on the component, and dont let me pick a new date,