After windows patching (windows 2008 R2 , SQL Server 2012 Sp2). I could not start SQL Server Service . I get error 1067 and this from the error log* The SQL Server Network Interface library could not deregister the Service Principal Name (SPN) for the SQL Server service. Error: 0x13, state: 2. Administrator should deregister this SPN manually to avoid client authentication errors." Yes it is a production system and any help is welcome. I tried using domain account that has sysadmin and local admin privilege.