jqgrid edit server response protocol

Question

I'm using jqgrid with PHP, not sure how to use handle server side edit. 'afterSubmit' is suppose to be called when user submits the edit form, but I'm unable to hook up with the response handler afterSubmit in the following php code. processResponse is never called. what's wrong?

$custom = setJSCode($custom);

// Enable navigator
$grid->navigator = true;

$grid->setNavOptions('navigator', array("excel"=>true,"add"=>true,"edit"=>true,"del"=\
>false,"view"=>true));
$grid->setNavOptions('edit',array('url'=>'save.php',"closeAfterEdit"=>true, \
"afterSubmit"=>"processResponse"));
$grid->setNavOptions('add',array('url'=>'save.php',"closeAfterEdit"=>true));
// Enjoy
$grid->renderGrid('#redirect_grid','#master_pager',true, null, null, true,true);

$conn = null;