The following steps are to be reviewed on the source server.
1. Reboot the source server.
2. In case backup job and VSS writers still fail, follow these steps:
Add the backup account in the following registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS\VssAccessControl Note: Right click on VSSAccessControl->Permissions.
Add backup account there and give it FULL control.
Also, make sure Administrators group is owner of this key.
3. Open a command prompt and type the command "Vssadmin list Shadows"
If a snapshot exists, it will be listed.
Before attempting to delete the snapshot make a note of the time at which it was taken.
This will help to determine if the orphaned snapshot was created during or outside a backup.
If the snapshot was created outside a backup, check for scripts or applications that could have created it (for example, some applications take snapshots by creating scheduled Windows tasks).
4. Use command "Vssadmin delete shadows /all" to delete the shadow copies.
5. Open Device Manager and go to View > Show Hidden Devices.
6. Expand Storage Volume Shadow Copies and uninstall all remaining shadow copies.
7. Reboot the server and re-try the backup job.