From time to time you can have a server restart or shutdown dirty causing windows to constantly show a shutdown error notification for everyone logging into server. To clear the error you can remove all the values in the registry located at the following location.
The value will be things like DirtyShutdown, LastAliveStamp, TimeStampInterval.
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Reliability
Restart and enjoy the peace of no error.