We have a Windows 2008 domain server which provides file service to our users. We add domain groups to the server local administrator group. We have realized those domain groups are all replaced with some string of characters such as S-1-5-21-873248931749837981732. We cannot even add any domain group or user to the local adminstrator group.
Experts, please advise if you know what is going on or how to fix this. If possible, we do not want the server to be reboot. Rejoining the server to the domain might fix the issue but that will require a reboot.