I have configured SQL Server 2008 R2 for mixed mode authentication on a Windows Server 2008 R2 box. I have logged in using domain administrator account into Windows as well as into Sql Server. Now I am trying to add another domain user account as a new login but I am getting the error saying “Windows NT user or group ‘\’ not found. Check the name again. (Microsoft SQL Server, Error: 15401)” though this user is present in domain. I am adding using Management Studio -> Logins -> New Login. When I search for the domain user using the search button the system searches successfully for the user but when I click ok button to create the login I get the above error. I have tried using T-SQL also to create the login but with the same error.
Need help!!
The problem was with SIDs. As we were using VMs the SID was the same and this was causing the error. After changing the SID using sysprep the problem got resolved.