I have an error from a Veeam Hyper-V backup of a Virtual Machine in a Hyper-V host:

Unable to create snapshot (Microsoft CSV Shadow Copy Provider) (mode: Veeam application-aware processing). Details: Writer 'Microsoft Hyper-V VSS Writer' is failed at 'VSS_WS_FAILED_AT_POST_SNAPSHOT'. The writer experienced a transient error. If the backup process is retried, the error may not reoccur. --tr:Failed to verify writers state. --tr:Failed to create VSS snapshot. --tr:Failed to perform pre-backup tasks.

I cannot understand if this is a host error, a guest error or Veeam error. I tried to reboot the VM but I got the same error. I did not try to reboot the host, but I tried to change the host (this VM is inside a failover cluster of two hosts) and with this change the backup works again.

During the backup failure I ran this command in the host:

 vssadmin list writers

The output was:

>    Writer name: 'Microsoft Hyper-V VSS Writer'
>        Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}
>        Writer Instance Id: {f50fe40b-27d6-4a98-8713-e5a1dce54c97}
>        State: [1] Frozen

After the VM migrates to another host, the writer state changes back to "Stable".

What can freeze the VSS writers?

There is a 10103 event in the Host:

Failed to revert to VSS snapshot on the virtual hard disk '\\?\Volume{29e16157-002f-4cb4-af58-c95acbd54be9}\' of the virtual machine 'srvshare1'.
  • On the guest what applications are running? IE SQL or Exchange? – Zapto Aug 27 '15 at 11:35
  • No, it is only a file share. – Tobia Aug 27 '15 at 11:36
  • What is the option "Enable application-aware image processing" set to? – Zapto Aug 27 '15 at 11:41
  • The option "Enable application-aware image processing" is flagged in the Veeam job. – Tobia Aug 27 '15 at 13:13
  • Disabling the Application-Aware Image Processing in this particular VM it works... however, should I disable it and ignore the error or it is better to solve this trouble with VSS? – Tobia Aug 27 '15 at 14:53

Is the virtual machine a domain controller?

Have you tried below from http://www.veeam.com/kb1697

vssadmin list writers

The results will appear as:

Writer name: 'NTDS' Writer Id: {b2014c9e-8711-4c5c-a5a9-3cf384484757} Writer Instance Id: {ee24b741-eaf7-4663-8f95-b92ae8c5e164} State: [1] Stable Last error: No error

If not listed as stable reboot the DC.

────────────────────────────────────────────────────────── Verify that Automatic mounting of new volumes enabled. ────────────────────────────────────────────────────────── From a Run command (Win+R) execute the command diskpart.

From within Diskpart run the following command.


If the results do not show “Automatic mounting of new volumes enabled.” Run the following command:

automount enable

────────────────────────────────────────────────────────── Verify that there are no .bak keys in the ProfileList within the Registry. ────────────────────────────────────────────────────────── From a Run command (Win+R) execute the command regedit.

Within the registry navigate to:

HKLM\Software\Microsoft\Windows NT\CurrentVersion\ProfileList

There will be a list of Keys, you must remove any ending in .bak

  • Unfurtunately I already tried this solution... but it did not work for me – Tobia Sep 1 '15 at 11:08

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