Error Message

\\\Hyper-V?Virtual?Machine\". Snapshot technology used: Microsoft Volume Shadow Copy Service (VSS).
A snapshot could not be created.  The most probable cause is a disk signature collision between two or more VHDs that are assigned to the virtual machine.

0xa0009650 - A snapshot could not be created.  The most probable cause is a disk signature collision between two or more VHDs that are assigned to the virtual machine.

Also seen error:

0xa0009651 - A snapshot could not be created.  The most probable cause is a disk signature collision between a VHD that is assigned to the virtual machine and physical disk mounted on the Hyper-v host. 

UMI Code: V-79-40960-38480 

1. The disk signatures of multiple disk of virtual machine's (vhd's) are colliding/same.
2. The Hyper-V writers on the host machine fail during the backup process.
3. Insufficient disk space on the VM.
4. Using multi path I/O configuration which creates two identical disks of which one is active and one is passive.

1. Check and Fix the Disk Signature Conflict. 

       To check Disk Signature or ID use the Windows DISKPART utility commands "detail disk" and "uniqueid".

       https://technet.microsoft.com/en-us/library/cc770877(WS.10).aspx

       Refer to the following image. The "Disk Id" should be unique.

        Contact Microsoft Support for further assistance changing the Disk Signature.

2. Check the writer status on the Hyper V host machine by running "VSSadmin list writers" command using command prompt:

         Reboot the server to check if the writers are in stable stable state, re-run the backup job.

         If writers continue to fail, Contact Microsoft Technical Support to resolve the issue with the writers.

3. Free up sufficient disk space in the VM if it's out of space. 

      4.  Additional driver may be needed for multi path I/O configurations (for details regarding multipath driver please contact your hardware vendor vendor)