0x800a1391 - JavaScript运行时错误:'PageMethods'是未定义的

我需要调用服务器端代码"c# Function"在我的asp.net项目在javascript，所以我使用这种方式:

<script type="text/javascript">
    function doReadPublicData() {
        PageMethods.btnVerifyPubData_Click(OnGetMessageSuccess, OnGetMessageFailure);
    }
    function OnGetMessageSuccess(result, userContext, methodName) {
        alert(result);
    }
    function OnGetMessageFailure(error, userContext, methodName) {
        alert(error.get_message());
    }
</script>

我在脚本管理器中启用了EnablePageMethods属性:

<asp:ScriptManager ID="ScriptManager1" EnablePageMethods="true" runat="server">
</asp:ScriptManager>
<asp:Button ID="btnVerifyPubData" runat="server" OnClientClick="doReadPublicData();"
    OnClick="btnVerifyPubData_Click" Text="Show Information"
    CssClass="submitButton" PostBackUrl="~/ParsePublicData.aspx" />

[WebMethod]
    public static void btnVerifyPubData_Jscript(string t)
    {
    }