Hello @everyone

I am using jQuery ajax to bind a html select list on an asp.net webform. The webmethod is executing absolutely fine but in error method as getting the above error. I searched on google and compare my code I found no differences. Please help me out of it below is my code.

        $(document).ready(function () {
            $.ajax({
                type: "POST",
                url: "ManPowerEntry.aspx/getProjectNames",
                dataType: "json",
                contentType: "application/json",
                success: function (res) {
                    $("#ddlProject").empty();
                    $("#ddlProject").append($("<option value='0'> --Select Project--</option>"));
                    $.each(res.d, function (key, value) {
                        $("#ddlProject").append($("<option></option>").val(value.projectCode).html(value.projectName));
                    });
                },
                error: function ajaxError(result) {
                    alert(result.status + ' : ' + result.statusText);
                }
            });
        });

        public class ProjectManPower 
        {       
            public string projectCode{ get; set; }
            public string projectName { get; set; }
        } 

        [WebMethod]
        public static List<ProjectManPower> getProjectNames()
        {
            string query = "select project_code, (project_code+' - '+ project_name) as ProjectName from ProjectMaster";
            DataTable dt = SqlConn.SqlExce.fillDataTableRet(query);
            List<ProjectManPower> lst = new List<ProjectManPower>();
            foreach(DataRow dr in dt.Rows)
            {
                lst.Add(new ProjectManPower
                {
                    projectCode = dr["project_code"].ToString(),
                    projectName = dr["ProjectName"].ToString()
                });
            }
            return lst;
        }