parameter not passing to webmethod

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C#

jQuery

HI,
I need to pass the parameter '999999999' to an webservice when i execute iam getting the error System.InvalidOperationException: Missing parameter: callerid.

pls help me out.

function SearchText() {
     $('#<%= txtusername.ClientID%>').autocomplete({
         source: function (request, response) {
             $.ajax({
                 type: "POST",
                 contentType: "application/json; charset=utf-8",
                 url: "../HttpHandler/Autocomplete.asmx/GetCallername",
                 data: "{'callerid':'" +9999999999+ "'}",
                 dataType: "json",
                 success: function (data) {
                     response(data.d);
                     alert('i enter');
                 },
                 error: function (result) {
                     alert("Error");
                 }
             });
         }
     });
 }

webservice :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using MSDataAccess;
using System.Data;

namespace Sun.HttpHandler
{
    /// <summary>
    /// Summary description for Autocomplete
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Autocomplete : System.Web.Services.WebService
    {

        [WebMethod]
        public string GetCallername(string callerid)
        {
            ConnectionCls clsConObj = new ConnectionCls();

            DataSet ds = null;
            string strPriorityOfCall = null;
            object[] obj = new object[6];
            obj[0] = 1;
            obj[1] = 1;
            obj[2] = 1;
            obj[3] = 1;
            obj[4] = 1;
            obj[5] = callerid;

            ds = DataAccess.ExecuteDataset(clsConObj.getConnectionString(), "sp_autoload", obj);
            if (ds.Tables[0].Rows[0]["CallerName"].ToString() != System.DBNull.Value.ToString())
            {
                return ds.Tables[0].Rows[0]["CallerName"].ToString();
            }
            else
            {
                return "User Doesnt Exist";
            }
        }
    }
}