The Windows Application Event Log inside the guest VM also shows the below Error Event at the time of failure:

Log Name:      Application

Source:            VSS

Event ID:          8193

Level:               Error


Volume Shadow Copy Service error: Unexpected error calling routine ConvertStringSidToSid.  hr = 0x80070539.


   OnIdentify event

   Gathering Writer Data


   Execution Context: Shadow Copy Optimization Writer

   Writer Class Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f}

   Writer Name: Shadow Copy Optimization Writer

   Writer Instance ID: {54d14cb1-7207-4405-9f53-19ed009ee5bd}


The issue may be caused by an invalid entry inside the following registry sub tree:

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


Beginning with Windows Vista and Windows Server 2008, the Shadow Copy Optimization Writer 

deletes certain files from volume shadow copies. This is done to minimize the impact of Copy-on-Write I/O during regular I/O on these files on the shadow-copied volume. The files that are deleted are typically temporary files or files that do not contain user or system state.


The SID being referenced in the event can not be resolved. This is due to a “.bak” entry inside the following registry sub tree:

HKey_Local_Machine\Software\Microsoft\Windows NT\CurrentVersion\ProfileList 


Removing the invalid entry from the registry will solve the problem.


  1. On the problematic machine, open the Registry Editor

  2. Browse to HKLM\Software\Microsoft\Windows NT\CurrentVersion\ProfileList

  3. Check for any entries that have a ".bak" value appended. If so, this may be cause the failure when trying to resolve the SID of the writer

  4. Please backup the registry key first, and then delete the entry with the extra ".bak"

  5. Reboot the problematic machine

  6. Re-try the backup

  7. If the above does not work, then please try to assign a drive letter to the boot partition and then remove it, and again re-try the backup.