Ajax does not work!

Ajax does not work!


I have this code:

         
          $.getJSON(site_url+'index/meciuri/event_id/'+event_id, function(data){
              alert(data);
              $('#grid').html(data);
             
          });
         
it alerts null ! Firebug shows me that it makes the request and it return a varios number of bytes 2,10, 700 etc.
But it doesn't display any results!!! In all browsers. I have tried also with $.get, $.post, $.ajax and even yui.
The same thing. I have written like a million ajaxes before!


Thanks.