C# 上下文已经在跟踪实体 Azure Active Directory 图形 API.添加组成员

我正在尝试将成员添加到 azure 活动目录组，但它失败了，它显示我以下错误。

上下文已在跟踪实体

我试图为它找到很多，我也看到了这个链接

Azure Active Directory 图形客户端 2.0 - 上下文当前未跟踪实体

http://blogs.msdn.com/b/aadgraphteam/archive/2014/12/12/announcing-azure-ad-graph-api-client-library-2-0.aspx

但我没有得到任何成功，请帮助我。

这是我的代码：

try
        {
            ActiveDirectoryClient client = ADGraphHelper.GetActiveDirectoryClient();
            IGroupFetcher groupFetcher = client.Groups.GetByObjectId(groupId);
            Group group = (Group)(await groupFetcher.ExecuteAsync());
            string[] userIds = userId.Split(',');
            foreach (string id in userIds)
            {
                if (id != "")
                {
                    IUser user = client.Users.Where(u => u.ObjectId == id).ExecuteAsync().Result.CurrentPage.ToArray().First();
                    if (user != null)
                    {
                        //check wather user aleady present into group or not
                        IDirectoryObject userExists = group.Members.Where(u => u.ObjectId == id).FirstOrDefault();
                        if (userExists == null)
                        {
                            group.Members.Add(user as DirectoryObject);
                        }
                    }
                    else
                        throw new Exception("User is null.");
                }
            }
            await group.UpdateAsync();
            return Json(new { success = true });
        }
        catch (Exception ex)
        {
            ModelState.AddModelError("", "we connot process your request please contact to support for more details.");
// error handling code.
            return PartialView();
        }