jQuery Grid Plugin - jqGrid

Hi, I'm trying to populate my grid using json, managed by php. The json response is ok, I see it in firebug. But it looks like loading, the overlay div never dissapears, and the grid is empty. (I don't receive javascript errors)

I'm using the lastest version (3.8.1)

My javascript code:

<script type="text/javascript">
$(document).ready(function(){
  $("#grid_recibidos").jqGrid({
    url:'admin/json_grid.php?q=grid_recibidos',
    datatype: 'json',
    mtype: 'POST',
    colNames:['ID','E-mail', 'Nombre','Mensaje','Respondido','Fecha'],
    colModel :[
      {name:'id', index:'id', width:55, jsonmap:"id"},
      {name:'email', index:'email', width:90, jsonmap:"email"},
      {name:'nombre', index:'nombre', width:80, align:'right', jsonmap:"nombre"},
      {name:'mensaje', index:'mensaje', width:80, align:'right', jsonmap:"mensaje"},
      {name:'respondido', index:'respondido', width:80, align:'right', jsonmap:"respondido"},
      {name:'fecha', index:'fecha', width:150, sortable:true, jsonmap:"fecha"}
    ],
    pager: '#grid_recibidos_pager',
    rowNum:10,
    rowList:[10,20,30],
    sortname: 'fecha',
    sortorder: 'desc',
    viewrecords: true,
    caption: 'Mensajes recibidos'
  });
});
</script>

And the json response:

{"page":1,"total":1,"records":2,"rows":[{"id":0,"cell":{"id":"1","email":"rgsrh","nombre": "sdgh","mensaje":"stdfjh","respondido":"0","fecha" :"2010-11-02"}},{"id":1,"cell":{"id":"2","email":"hhhh","nom bre":"jjj","mensaje":"kkk","respondido":"0","fecha ":"2010-11-02"}}]}

Any ideas?? Thanks