autocomplete data from webserive

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ASP.NET

Javascript

hi everyone, i have created small application, in my application i have text box, i ll fill the data to the text box by using web service which is in my hosted my PC,
i am using java script code for the auto complete process, below is my code,

$.ajax({
                type: "POST",
                url: "http://localhost/kff/n_kff.asmx/getitem",
                dataType: "json",
                data: "{}",
                contentType: "application/json; charset=utf-8",
                success: function(data) {
                    var datafromServer = data.d.split(":");
                    $("[id$='txtautofromDB']").autocomplete({
                        source: datafromServer
                    });
                },
                error: function(XMLHttpRequest, textStatus, errorThrown) {
                    alert(textStatus);
                }
            });

this is my code for autocomplete in text box with web service, but the above code is not working , please tell me what changes should i want to do in the above code,, your help will be great-full to me