[jQuery] jsonp problems

[slava]

Hello,
I am having problems using jquery's cross domain json function.
I send a request like this:

var data = { 'data':  '10' };
$j.ajax({
                dataType: 'jsonp',
                data: data,
                url:  'http://another-domain/json-echo.php?jsoncallback=?',
                success: function(json){
                        alert("received back: " + json);
                }
        });

and on the json-echo.php

$val = json_decode($_REQUEST['data'], true);
$output = json_encode($val);
echo $_REQUEST['jsoncallback'].'('.$output.')';

I get alert box with:
received back: 10

going any more complex with the data that I send always fails to
decode properly and i get a null back
so if set
data = {
               'data':
                        { 'url' : 'someurl' }
            };
if fails... I've struggled with this all day trying all could think of
with no luck so far. Please help me get this working. :)

thank you
Slava