jQuery Grid Plugin - jqGrid

Hello everyone!

I'm returning an JSON result from my Php file and when i try 

$("#grid").addJSONData(eval("("+ret.responseText+")"));

I get addJSONData is not a function! Anybody please help!!!

Thank you in advanced!

OBS: Here is my code

$("#list").jqGrid({

       datatype:

function()

{

var dados  = 

{

func:  "listagem",

view:  "usuarios"

}

$.ajax({

type: "POST",

url: "../app/config/ajax.php",

data: dados,

datatype: "json",

complete: function(ret){

$("#list").addJSONData(eval("("+ret.responseText+")"));

},

error: function()

{

alert('erro ajax')

}

});

},

       colNames:['Nome','Login', 'Data de Cadastro'],

       colModel :[ 

       {name:'nome',index:'nome', width:55, sorttype:'string'}, 

       {name:'login',index:'login', width:80, sorttype:'string'}, 

       {name:'data_cadastro',index:'data_cadastro', width:150, align:'right',sorttype:'date'}

],

       pager: jQuery('#pager'),

       rowNum:10,

       viewrecords: true,

       imgpath: '../externos/js/themes/basic/images',

       caption: 'Usuários'

});