C#关于js调用后台方法的问题

我想在sendMes()中调用SendMessage()为什么不成功，那位高手帮忙解答一下。谢谢。
后台代码
   
        /// <summary>
        /// 注册页面js
        /// </summary>
        protected void RegeditPageFunction()
        {
            StringBuilder strScript = new StringBuilder();
            strScript.AppendLine("function sendMes(a)");
            strScript.AppendLine("{");
            strScript.AppendLine("var isSend = confirm(\"是否发送祝福？\")");
            strScript.AppendLine("if(isSend==true)");
            strScript.AppendLine("{");
            strScript.AppendLine("var fun = \"<%=SendMessage('\"+a.name+\"');%>\";");
            strScript.AppendLine("alert(fun);");
            strScript.AppendLine("}else{");
            strScript.AppendLine("return false;");
            strScript.AppendLine("}");
            strScript.AppendLine("}");
            Page.ClientScript.RegisterStartupScript(this.GetType(), "aaa", strScript.ToString(), true);
        }
        public string SendMessage(string getPerson)
        {
            //using (SPWeb web = SPContext.Current.Site.OpenWeb())
            //{
            //    SPList list = web.GetList(LeaveUrl);
            //    SPListItem listItem = list.Items.Add();
            //    listItem["标题"] = LeaveMes;
            //    listItem["留言时间"] = DateTime.Now;
            //    listItem["发送人"] = SPContext.Current.Web.CurrentUser.LoginName;
            //    listItem["接收人"] = getPerson;
            //    listItem["内容"] = LeaveMes;
            //    listItem["悄悄话"] = "否";
            //    listItem["回复记录ID"] = "0";
            //    listItem.Update();
            //}
            return getPerson;
        }