The following is what I am using in my code and it displays the ugly looking alert:

$.ajax({
                type: 'POST',
                url: "Default.aspx/SetSession",
                data: '{ "name" : "' + name + '" }',

                cache: false,
                async: false,

                contentType: 'application/json; charset=utf-8',
                dataType: 'json',

                success: function (result) {
                    alert("File uploaded successfully...");
                },
                error: function (result) {
                    alert("Failed to upload file...");
                }

            });