web api 提交调用

使用cloud的web api 的提交方法，程序调用成功，但是返回值j["Message"]：Null。代码如下

ApiClient client = new ApiClient("http://192.168.1.159/K3Cloud/");

object[] loginInfo = new object[] {
"57be588eb77d9e",//帐套Id
"demo",//用户名
"111111",//密码
2052};//语言id
var ret = client.Execute("Kingdee.BOS.WebApi.ServicesStub.AuthService.ValidateUser", loginInfo);
var result = JObject.Parse(ret)["LoginResultType"].Value();
if (result == 1)
{
JObject obj = new JObject();
obj.Add("CreateOrgId", "0");
obj.Add("Numbers", " 'E20160921001.' ");

ret = client.Execute("Kingdee.BOS.WebApi.ServicesStub.DynamicFormService.Submit", new object[] { "xcc_expenses", obj.ToString() });
JObject j = JObject.Parse(ret);
return ResponseJsonHelper.GetSuccessJson(j["Message"]);
}
return ResponseJsonHelper.GetSuccessJson("");
}

请总部老师帮忙指导，超看下原因。