<httpModules>
   <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
</httpModules>

ScriptMethod(ResponseFormat = ResponseFormat.Json)]
[WebMethod]
/// <summary>
/// 是否允许注册
/// </summary>
/// <param name="MemberLoginID"></param>
/// <returns></returns>
public static MemberInfo AllowRegist(string MemberLoginID)
{
    return new MemberInfo();//由于设置了返回类型是JSON,所以客户端的JQ能够识别
    // MemberInfoBLL mi = new MemberInfoBLL();
    //if (!mi.ExistMember(MemberLoginID))
      //return "{d:true}";//我测试发现,客户段在接收数据的时候,会多了2个双引号,导致转换JSON格式失败..郁闷
    //else
      //return "{d:false}";
}

$.ajax({
    cache:false,
    type: 'POST',
    contentType: 'application/json; charset=utf-8',
    data: "{'MemberLoginID':'" + $("#<%=MemberLoginID.ClientID %>").val() + "'}",
    dataType: 'json',
    url: 'Reg.aspx/getDate',
    success: function(result,x,y) {
      alert(result);
    },
    beforeSend:function (xhr) {
      xhr.setRequestHeader('If-Modified-Since', '0');
      //this; // 调用本次AJAX请求时传递的options参数
    },
    error: function(e) {
      debugger; //alert("可能服务器忙没有返回数据，请重试");
    }
});