I have a JavaScript Ajax call (jQuery.ajax), that does not execute the success callback function.

$.ajax({
        url: target,
        contentType: 'application/json; charset=utf-8',
        type: 'POST',
        // type: 'GET',
        dataType: 'jsonp',
        error: function (xhr, status) {
            alert(status);
        },
        success: function (result) {
            alert("Callback done!");
            // grid.dataBind(result.results);
            // grid.dataBind(result);
        }
    });

I see in firebug, that the request is posted and the correct result in terms of the json is returned as expected. What is wrong?