jquery ajax获取回传数据获取不到,该如何解决

<script type="text/javascript">    function AddUser() {        var userName = $("#txtUserName").val();        var Email = $("#txtEmail").val();        var dpost = "{action:\"AddUser\",UserName:\"" + userName + "\",Email:\"" + Email + "\"}";        alert(dpost);        $.ajax({            url: "Ajax/UserAjax.aspx",            data: dpost,            dataType: "JSON",            success: function (result) {                alert(result);            },            error: function (XMLHttpRequest, textStatus, errorThrown) {                alert(XMLHttpRequest.status);                alert(XMLHttpRequest.readyState);                alert(textStatus);            }        });    }</script>    <input type="text" id="txtUserName" /><br />    <input type="text" id="txtEmail" /><br />    <asp:Button ID="btnAdd" runat='server' Text="添加" OnClientClick="AddUser();return false;" />

protected void Page_Load(object sender, EventArgs e)        {            if (Request["action"] != null)            {                string action = Request.Form["action"].ToString();                if (action == "AddUser")                {                    try                    {                        string userName = Request.Form["UserName"];                        string email = Request.Form["Email"];                        DataSet dsUser = Application["dsUser"] as DataSet;                        DataRow drUser = dsUser.Tables[0].NewRow();                        drUser["userName"] = userName;                        drUser["Email"] = email;                        dsUser.Tables[0].Rows.Add(drUser);                        Application["dsUser"] = dsUser;                        Response.Write("ok");                    }                    catch                    {                        Response.Write("Add Error");                    }                }            }        }