VSS based backups/restores may fail with various AOFO initialization errors. Windows Application log on the affected server may report various VSS related errors/warnings like, Event ID 20 or Event ID 8193 for event source "VSS". Description for event ID 20 and Event ID 8193 is shown in section 1 and Section 2 respectively:

Section 1.

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Volume Shadow Copy Service error: A critical component required by the Volume Shadow Copy service is not registered.  This might happened if an error occurred during Windows setup or during installation of a Shadow Copy provider.  The error returned from CoCreateInstance on class with CLSID {faf53cc4-bd73-4e36-83f1-2b23f46e513e} and Name VSSEvent is [0x80040154]
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Section 2.

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Volume Shadow Copy Service error: Unexpected error calling routine CoCreateInstance.
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To confirm the status of VSS writers, on the affected server run vssadmin list writers from command prompt. It may not show some/any writers at the prompt.


If the writers are not listed follow the steps listed below in Section A and Section B.

Note: The list below includes configuration changes that have been provided by our customer base to resolve VSS related issues. It is advisable to consult Microsoft before making the changes below:

Section A:

To register / re-register Microsoft Shadow Copy Provider and Volume Shadow Copy Services DLLs


1. Open a command prompt (Start>Run>CMD).

2. Execute the following commands:

Net stop vss
Net stop swprv

3. Change directory to \windows\system32  (i.e.: cd C:\windows\system32)

4. Register the below mentioned .dll files by executing the following commands:

regsvr32 ole32.dll
regsvr32 vss_ps.dll
vssvc /Register
regsvr32 /i swprv.dll
regsvr32 /i eventcls.dll
regsvr32 es.dll
regsvr32 stdprov.dll
regsvr32 vssui.dll
regsvr32 msxml.dll
regsvr32 msxml3.dll
regsvr32 msxml4.dll

5. Execute the following commands:

Net Start vss
Net Start swprv

6. Re-run the command vssadmin list writers.

If VSS issue still persists refer to the following Microsoft KB article

 http://support.microsoft.com/kb/940032

After following Section A if the issue still persists, follow Section B.

Section B:

1. Stop the Microsoft Shadow Copy Provider &Volume Shadow Copy Service.

2. Export the contents of the HKLM\Software\Microsoft\EventSystem key to a .regfile.

Warning:Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.

3. Delete the HKLM\Software\Microsoft\EventSystem\{26c409cc-ae86-11d1-b616-00805fc79216}\Subscriptions key. (Do not delete the EventClasses key).

4. Restart the server.

5. Run the"VSSADMIN LIST WRITERS" command.

This causes the VSS entries in the HKLM\Software\Microsoft\EventSystem\{26c409cc-ae86-11d1-b616-00805fc79216}\Subscriptions key to be rebuilt when the writers initialize.