What does the ajax param mean in your example? In order to set a param you would have to use a syntax like
array('menu/delete','ajax'=>'someValue')
//In your case
echo CHtml::ajaxSubmitButton('Delete selected',array('menu/delete','ajax'=>'yw0'));
Just keep in mind that you are obviously setting auto created widget ids as params (yw0). You should assign your own ids to widgets, otherwise another widget could have the same id and that can be hard to debug