请求帮助：ajax调用后台方法返回页面显示为undefined

前台代码：
function start() {
$.ajax({
//要用post方式
type: "Post",
//方法所在页面和方法名
url: "Second.aspx/SelectAll",
contentType: "application/json; charset=utf-8",
dataType: "html",
success: function (data) {
t = "<table>";
t += "<tr>";
t += "<td>员工编号</td><td>员工姓名</td><td>工作</td><td>上级编号</td><td>受雇日期</td><td>薪金</td><td>佣金</td><td>所属部门</td><tr>";
$.each(data, function (i, item) {
t += "<tr>";
t += "<td>" + item.EMPNO + "</td>";
t += "<td>" + item.ENAME + "</td>";
t += "<td>" + item.JOB + "</td>";
t += "<td>" + item.MGR + "</td>";
t += "<td>" + item.HIREDATE + "</td>";
t += "<td>" + item.SAL + "</td>";
t += "<td>" + item.COMM + "</td>";
t += "<td>" + item.DEPTNO + "</td>";
t += "</tr>";
});
t += "</table>";
$("#table").html(t);
},
error: function (err) {
alert(err);
}
});
}
后台代码：
[WebMethod]
public static string SelectAll()
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
//接收查询结果
List<EMP> list = EMPManager.SelectAll();
//将结果转换成Json字符串
string result = serializer.Serialize(list);
return result;
}[WebMethod]
public static string SelectAll()
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
//接收查询结果
List<EMP> list = EMPManager.SelectAll();
//将结果转换成Json字符串
string result = serializer.Serialize(list);
return result;
}