京东WebService调用 求助~~~~~

请教各位  为什么这样调用获取不到数据

 string venderSign = ""; //签名
 string tradeno = DateTime.Now.Ticks.ToString();//流水号
 long venderID = 20388; //商家ID
 string secretcode = "08D434A563ABE0712B8DCD15B762D33C"; //商家key
 venderSign = MD5.Encrypt(secretcode + venderID.ToString() + tradeno + secretcode,32); //MD5加密
 string startDate="2011-03-01 00:00:01"; //开始日期
 string endDate="2011-03-28 00:00:01"; //终止日期
 string field = "venderId,orderState";

 JD.OrderSearchServiceImplService s = new jingdong.JD.OrderSearchServiceImplService();
 JD.apiOrderQueryDetail detail = s.searchOrderInfo(venderSign, tradeno, venderID, startDate, endDate, "ALL", "100", "20", field);
string dfds = detail.apiResult.chineseErrCode;
bool t = detail.apiResult.success; //这里返回的为true

int total = detail.orderTotal; //为什么这儿没有订单信息 返回的总订单数为0



请问各位，是什么原因导致的？？？