Hyper-V Virtual Machine backup job fails with VSS snapshot failure error V-79-40960-38521

Problem

Running the Hyper-V virtual machine backup job fails with VSS snapshot failure error as shown below

Error Message

The Backup Exec Job log shows the following error message:

Final error: 0xa0009679 - A failure occurred querying the Writer status for a Hyper-V virtual machine. See the job log for details about the error.

For additional information regarding this error refer to link V-79-40960-38521 

V-79-40960-38521 - Snapshot Technology: Initialization failure on: "VRTSRV::\\<Hyper-V Host name or IP\Hyper-V?Virtual?Machine\<Virtual Machine Name>". Snapshot technology used: Microsoft Volume Shadow Copy Service (VSS).

A virtual machine snapshot could not be created. Use the Event Viewer on the Hyper-V host to identify the cause. If the virtual machine is not properly configured, it may be necessary to use the Event Viewer in the virtual machine to identify the cause.
 

IMPORTANT:

This article only applies when in addition to the above error message the following error code is mentioned within the event logs of the Hyper-V Host and the VM which gets backed up:
0x800423F2

On the Hyper-V host:

Event ID: 10172
VSS writers inside virtual machine '<Name of VM>' failed to perform BackupComplete to its shadow copy (VSS snapshot) set: The writer's timeout expired between the Freeze and Thaw events. (0x800423F2). (Virtual machine ID 00AE1346-040D-4563-B23C-1AC6B61713A1)

On the guest OS being backed up:

Event ID: 2
The VSS writer ASR Writer failed with status 9 and writer specific failure code 0x800423F2

Cause

The issue occurs because the VSS encounters a deadlock during the Thaw event if the Security Account Manager (SAM) has pending writes for the registry. Microsoft has confirmed this problem in KB 2996928 article and have released a hotfix.
 

Solution

Install the Microsoft Hotfix 2996928 for Windows Server 2012/2012 R2/2008 R2 on the Hyper-V host and guest Virtual Machines having this issue and then run the virtual machine backups.

NOTE: The HotFix mentioned above is also part of 'optional' Update Rollup 3013769 for Windows 2012 R2. Link to Update Rollup is KB 3013769
 

NOTE: If above mentioned Hotfix does not resolve the issue and for Windows version 2016 and 2019 please review article Troubleshooting 0xa0009679 / V-79-57344-38521 with Backup Exec Hyper-V backups