Event Id 12 is logged in the system log when you backup a hard disk on a Windows Server 2008 machine. Backup job runs, and the following error message is being shown in the system log of the event viewer:
System Log entry:
Log Name: System
Event ID: 12
Task Category: None
Computer: computer name
The device 'MSFT Virtual HD SCSI Disk Device' (SCSI\Disk&Ven_MSFT&Prod_Virtual_HD\GUID) disappeared from the system without first being prepared for removal.
This event listed in the system log is a typical Windows event that would be seen for a backup using hot add & Windows 2008. This is due to the adding and removing of the virtual disk to/from the virtual machine with vRanger outside of the OS of the vRanger machine.
***vRanger is not able to request for a removal of the disk during the unmounted via the Windows OS installed on the vRanger machine, and only by the ESX server. ***
The error message can be disregarded/ignored since this is expected behavior with hot add working on a W2K8 machine.
Microsoft KB for review/reference: