How to response a proper server execution to Ajax Post method?

How to response a proper server execution to Ajax Post method?

I have a very simple task in my application, wich retrieves data from a
combobox in after its selection event.
When select event is raised, data is passed to a jQuery function which
requests opperation from server side.
All these stuffs are ok, but on processing server's response, Ajax
receives a fail condition to the request. As I'm a rookie in jQuery and
Ajax, I didn't know what I should be missing or doing wrong.
Jsp piece:
<input id="updStatus"
class="easyui-combobox"
name="updStatus"
data-options="
valueField:'id',
textField:'Name',
url:'StatusListCombo',
onSelect:function updStatusTask(row){
$.fn.updStatusTask(row.id, ${task.id});
}">
jQuery function:
$.fn.updStatusTask =
function (idStatus, idTask){
var result = $.post("TaskUpdateStatus", {
idTask : idTask,
idStatus : idStatus
}
);
result.done(function( data ) {
alert("data: " + data); //<--NOT REACHED!!
});
result.fail(function(jqXHR, textStatus) {
alert("fail data: " + textStatus); //FIRED
});
result.always(alert("always"));//FIRED
};
Serverside method:
@RequestMapping(value = "/TaskUpdateStatus")
public String TaskUpdateStatus(Long idTask,
Long idStatus,
HttpSession httpSession,
HttpServletResponse resp) throws IOException {
String result = new String();
try{
//... do DAO opperations to persist, everything Ok...
resp.setStatus(200);
result = "Task successfully updated.";
}
catch(Exception e){
result = "Error: " + e.getMessage();
}
return result;
}