[jQuery] not returning a JSON object

[defdev]

Hi,

i have a form defined as follows:

$(document).ready(function(){
        $('#edit_page_form').ajaxForm({
                type: "POST",
    timeout: 45000,
          dataType: 'json',
    error: function() {
            alert("error etc ");
          },
          success: function(json) {
            alert(json);
            alert(json.message);
          },
          complete: function() {
                alert('done');
          }
  });
});

when alerting json in the success function - it echoes out the Json as
a string, and not a valid object - hence, json.message doesnt work/is
undefined.

from the server side:

 echo '{ message: "why wont this work" }';


im using jquery 1.7.2.

is there something obvious i am missing?

cheers
Joe