Domain Admins can't connect to SQL Server I have a Windows Server 2012 R2 domain controller and a database server (W2K12R2/SQL Server 2012).

As allowed usergroup I have given the group "domain-admins" sysadmin rights.

But somehow any domain-administrator can't connect to that SQL Server, but when I add the domain-administrator user directly as allowed user it does work.
The active directory does work. RDP-Login works. Am I missing something?

Does anybody know how to grant access to the whole group "domain-admins"?

The error message is:

Servername: SRV-DB
Error Number: 18456
Schweregrad: 14
Status: 1
Line of Code: 65536

In the event log it says (translated):


  Error checking the token based server access with infrastructure failure.


State is "1" . I log on to that db-server with RDP as an domain-admin. I have to explicitly start SSMS with "run as administrator". Then I can access the "localhost". If I leave out starting SSMS as admin then I can't do that. I thought being in the group "domain-admins" would be enough.
I found the answer to my problem in this answer by Remus Rusanu.

As an domain-admin connected to that SQL-Server-Host via Remote Desktop. I had to start SQL Server Management Studio explicitly "as an administrator". (right-click -> run as administrator). 

If SSMS isn't started in administrator mode, the current login is not in "builtin\administrators"-group. That was the problem.

It comes from Windows user access control (UAC). So that is actually a security "feature".