When attempting a backup using Backup Exec 2010 R2 the following error may be seen:

" - AOFO: Initialization failure on: "\\server.domain.com\Shadow?Copy?Components". Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).
V-79-10000-11226 - VSS Snapshot error. The Microsoft Volume Shadow Copy Service (VSS) snapshot provider selected returned: "Unexpected provider error". Ensure that all provider services are enabled and can be started. Check the Windows Event Viewer for details.
The following volumes are dependent on resource: "C:" "D:""

The VSS writers may also show "State: [9] Failed" or "State: [10] Failed":

C:\>vssadmin list writers
vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool
(C) Copyright 2001 Microsoft Corp.

Writer name: 'System Writer'
   Writer Id: {e8132975-6f93-4464-a53e-1050253ae220}
   Writer Instance Id: {7f0448a5-aedd-4393-81b4-d3f2f74dcf68}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'COM+ REGDB Writer'
   Writer Id: {542da469-d3e1-473c-9f4f-7847f01fc64f}
   Writer Instance Id: {d4e192ca-bf8b-4b79-94f3-ae3b33fd7756}
   State: [1] Stable
   Last error: No error

Writer name: 'IIS Metabase Writer'
   Writer Id: {59b1f0cf-90ef-465f-9609-6ca8b2938366}
   Writer Instance Id: {1d51fe59-fada-4398-a277-091f2bf4aec3}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'NTDS'
   Writer Id: {b2014c9e-8711-4c5c-a5a9-3cf384484757}
   Writer Instance Id: {6487d956-7379-40f9-ae69-fc2395af6fb9}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'Event Log Writer'
   Writer Id: {eee8c692-67ed-4250-8d86-390603070d00}
   Writer Instance Id: {12be270c-79b8-454a-8462-011c53f477e7}
   State: [1] Stable
   Last error: No error

Writer name: 'Dhcp Jet Writer'
   Writer Id: {be9ac81e-3619-421f-920f-4c6fea9e93ad}
   Writer Instance Id: {8f58e3ec-3962-47ea-8650-f18cd8916ebe}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'WINS Jet Writer'
   Writer Id: {f08c1483-8407-4a26-8c26-6c267a629741}
   Writer Instance Id: {a2b28801-ba9a-4128-8098-804d77ca7b1a}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'TermServLicensing'
   Writer Id: {5382579c-98df-47a7-ac6c-98a6d7106e09}
   Writer Instance Id: {5f3c481d-3783-4752-b7e0-05bfc0443be0}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'WMI Writer'
   Writer Id: {a6ad56c2-b509-4e6c-bb19-49d8f43532f0}
   Writer Instance Id: {7a0ff4d4-9e18-4a45-8989-90d751f7be1f}
   State: [9] Failed
   Last error: Retryable error

Writer name: 'MSDEWriter'
   Writer Id: {f8544ac1-0611-4fa5-b04b-f7ee00b03277}
   Writer Instance Id: {c767313b-faaf-478d-8c2e-82d43893dffc}
   State: [1] Stable
   Last error: No error

Writer name: 'Registry Writer'
   Writer Id: {afbab4a2-367d-4d15-a586-71dbb18f8485}
   Writer Instance Id: {702bf63a-56dc-40ab-bb32-79b41e89a669}
   State: [1] Stable
   Last error: No error

Writer name: 'FRS Writer'
   Writer Id: {d76f5a28-3092-4589-ba48-2958fb88ce29}
   Writer Instance Id: {2c04f9ee-f1c1-488d-bd51-91bac80d4447}
   State: [9] Failed
   Last error: Retryable error

The BackupExec VSS provider is installed, as well as the Microsoft VSS Provider:

C:\>vssadmin list providers
vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool
(C) Copyright 2001 Microsoft Corp.

Provider name: 'Backup Exec VSS Provider'
   Provider type: Software
   Provider Id: {5fdb6ef5-6ead-4610-995b-401c88626115}
   Version: 1.0

Provider name: 'Microsoft Software Shadow Copy provider 1.0'
   Provider type: System
   Provider Id: {b5946137-7b9f-4925-af80-51abd60b20d5}
   Version: 1.0.0.7

The Backup Exec VSS Provider needs to be removed. Delete the associated registry key for the Provider Id. For the example above:

C:\>REG DELETE "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS\Providers\{5fdb6ef5-6ead-4610-995b-401c88626115}" /F

Restart the Volume Shadow Copy Service:

C:\>net stop vss
The Volume Shadow Copy service is stopping.
The Volume Shadow Copy service was stopped successfully.

C:\>net start vss
The Volume Shadow Copy service is starting.
The Volume Shadow Copy service was started successfully.

http://eventlookup.veritas.com/eventlookup/EventLookup.jhtml?EvtID=V-79-10000-11226

How to troubleshoot virtual machine VSS snapshot and quiesce issues during VMware backups
http://www.symantec.com/docs/TECH129724

How to perform an automated or manual uninstall of the Backup Exec Remote Agent for Windows Systems (RAWS) and BE VSS Provider - in 2010 and 2010 R2 ONLY
http://www.symantec.com/docs/TECH130940

The Volume Shadow Copy Service may leak private bytes and virtual memory when you use the service to take frequent snapshots in Windows Server 2003 or in Windows XP (VSS Version 5.2.3790.4120)
http://support.microsoft.com/kb/940252