Numerous backup jobs run by Symantec Backup Exec or Symantec System Recovery are dependent on Microsoft’s Volume Shadow Copy Service, (VSS). VSS is used to create snapshots of data that is to be backed up. VSS was introduced with Windows XP and Server 2003. The following backup jobs use VSS:

1. All System State backups of Windows Server 2003 and higher systems.
2. All Shadow Copy Component backups of Windows Server 2003 and higher systems.
3. All File backups using Advanced Open File Option (AOFO) of Windows Server 2003 and higher systems
4. All File backups of Windows 2008 and higher, (With or without AOFO enabled in the job)
5. All backups of Microsoft Exchange 2007 and 2010
6. Backups of Microsoft Exchange 2003 that have AOFO selected in the job (Not recommended)
7. Backups of Microsoft SQL that have AOFO selected in the job (Not recommended)
8. Backups of Microsoft SharePoint that have AOFO selected in the job (Not recommended)
9. Backups of Microsoft Hyper-V Virtual Machines
10. GRT functionality of the VMware Agent

Backup Exec and Symantec System Recovery act as VSS requestor in the snapshot process.

For more information about the components used to make a VSS snapshot:
http://technet.microsoft.com/en-us/library/cc785914(WS.10).aspx
http://www.symantec.com/docs/TECH130817

The first step in troubleshooting any snapshot error is to determine what is being backed up. To clarify the issue, determine the following:

• What resource is being backed up?
• Where does the resource reside?
• When does the backup happen?
• Once this has been established you can proceed to the event viewer of the problem system to collect more information.

VSS Writer Errors

To check Writer Status in a command prompt type  vssadmin list writers

• http://support.microsoft.com/kb/826936
• http://www.symantec.com/docs/TECH74515

To check to see if there are any other VSS providers installed on the server run vssadmin list providers at the command prompt.

• http://technet.microsoft.com/en-us/library/dd364887(WS.10).aspx

How to enable/disable Backup Exec verbose debug logging
http://www.symantec.com/docs/TECH37110

Common Articles Tech Notes

Microsoft VSS Fixes and Updates:
Windows Server 2003:
http://support.microsoft.com/kb/887827

Windows Server 2008 and SP2:
http://support.microsoft.com/kb/975928
http://support.microsoft.com/kb/975688
http://support.microsoft.com/kb/983425
http://support.microsoft.com/kb/953531

VSS Diagnostics
http://msdn.microsoft.com/en-us/library/aa384631(v=vs.85).aspx

System State or Shadow Copy Component backup fails with VSS snapshot error.
http://www.symantec.com/docs/TECH140909

Error message when you run the "vssadmin list writers" command on a Windows Server 2003-based computer: "Error: 0x8000FFFF"
http://support.microsoft.com/kb/940184/en-us

How to troubleshoot "AOFO: Initialization failure" errors for "Microsoft Volume Shadow Copy Service (VSS)" service during Backups/Restores
http://www.symantec.com/docs/TECH64330

Additional troubleshooting steps for Microsoft VSS errors when backing up Exchange 2007 database.
http://www.symantec.com/docs/TECH126543

Backups appear to hang when attempting to create a Snapshot using VSS (Volume Shadow Copy Service)
http://www.symantec.com/docs/TECH59155

An unexpected error occurred when cleaning up snapshot volumes. Confirm that all snapped volumes are correctly resynchronized with the original volumes.
http://www.symantec.com/docs/TECH38338

0xe000959b, VMware is unable to create a snapshot due to the freeze or thaw script used for preparing the guest operating system for the snapshot is not called correctly from VMware.
http://www.symantec.com/docs/TECH136415

Important This article is not for use with Windows Vista, with Windows Server 2008, or with later Windows operating systems. Starting with Windows Vista and with Windows Server 2008, Windows component installation is manifest-based. Trying to manually register specific components, as described in the following steps, can have unexpected results that may require you to reinstall Windows to resolve.

Don’t reregister dll’s on Windows 2008 or 2008 R2:
Beginning with Windows Vista and Windows Server 2008, Windows component installation is manifest based, and most of the registry is locked down even to Administrator. However, the VSS binaries in Windows Vista and Windows Server 2008 still contain the code to perform self-registration. The code is removed in Windows 7 and 2008 R2.  We don't suggest you to re-register VSS binaries in Windows Vista and Windows Server 2008 or later operating systems.  For more information please contact Microsoft, or refer to their documentation.
http://social.technet.microsoft.com/Forums/en/windowsserver2008r2general/thread/062cc52c-899b-45f3-8d0c-798b92363f41