I noticed I was getting 10 errors with the source VSS and ID of 12289 once a day. The error message is:


Volume Shadow Copy Service error: Unexpected error VSS_E_WRITER_STATUS_NOT_AVAILABLE. An older active writer session state is being overwritten by a newer session. The most common cause is that the number of parallel backups has exceeded the maximum supported limit. hr = 0x80042409.

Operation:

PostSnapshot Event

Context:

Maximum supported sessions: 64

Completed sessions: 8

Active sessions: 64

Aborted sessions: 0

Writer failed sessions: 0

New snaphot set: {9e27fa3a-58c4-49e8-ac98-e61ce47e227b}

Old snapshot set: {78b24809-c91f-46d2-ae15-1e3ac517f17c}

Old operation: 1014

Old state: 1

Old failure: 0

Execution Context: Writer

Writer Class Id: {e8132975-6f93-4464-a53e-1050253ae220}

Writer Name: System Writer

Writer Instance ID: {0ded508e-db13-4a3d-ae21-c82dde65cef3}

VSS Event 12289

VSS Event 12289

Each of the 10 events was a different “Writer Name
This is a simple problem, which means that my VSS writers, which handle Shadow Copies as well as Windows Backup, were busy when requested for use.
This is simply a conflict with backup schedules. I h to task manager and sure enough, the VSS was scheduled to make copies at 7 AM of drives C and D.
I have my Windows Server Backup scheduled at 7 AM as well. Moving the Windows Server Backup scheduled time to 6 AM solves this problem.
Alternately, you could move your VSS Shadow Copy Schedule to another time using Task Manager.

I also added Backup Operators Group read permissions on Volume Shadow Copy using GPMC. Create and link a new GPO, navigate to Computer>Windows>Security>System Services>Volume Shadow Copy. Enable the GPO, and set to automatic. Then click the Edit Security button, and add Backup Operators with read permissions.

I would like to point out that Microsoft and others have stated that this issue may be benign and cause no problems. My Backups are ALL completing successfully despite the error.

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