Possible Cause 1:
Windows 2012 R2 Datacenter edition OS layer in Hyper-V hit the Windows boot error “0xc000000e A required device isn’t connected or can’t be accessed” after the third reboot during Windows setup.
Using an Italian language pack and never followed the NLS boot disk steps.
Possible Cause 2
Caused by the boot manager and boot loader device being set to “unknown”: https://support.microsoft.com/en-us/kb/2261423
Possible Cause 3
When you perform a new installation of Windows Server 2008 R2 from a DVD to unallocated space, two partitions are created. During a recovery operation, the contents of the Boot folder are first restored from the ASR Writer backup and then restored again from the backup on drive C. This double restore action causes an inconsistency in the drive GUID definitions within the Boot folder data. This inconsistency leads to the boot error.
Possible Cause 5
PVS server ran out of storage space.
Image on vDisk became corrupt.
Possible Cause 6:
NLS file (international code page) that Windows wants is not on the boot image, which means Unidesk didn’t recognize it during our boot analysis. When you import an OS layer, Unidesk reads the list of drivers and services to determine what needs to be on the boot image and what can wait until layers are available. Unfortunately, NLS files are not recognized. We automatically include only US and Western Europe code pages.
Possible Cause 7:
Corruption on old vDisk version