[jQuery] Autocomplete plugin not working with $.ajax?

[Teddy Hong]

here the code
// if I type like below code, auto complete it's show..
$('#edit-submitted-order-no').autocomplete(["one","two","three"]);


// but if I type like below code, auto complete not showing... why?
anybody can help?... thanks
$.ajax({
        type: "POST",
        url: "test.php",
        success: function(msg){
            //alert(msg); return ["one","two","three"]
            $('#edit-submitted-order-no').autocomplete(msg);
        }
    });