VSS Error during a backup in Comet Backup: Another shadow copy creation is already in progress. Wait a few moments and try again.

Symptoms

Backup jobs complete with a Warning status instead of Success:

CONFIG_TEXT: VSS Error: Couldn't take snapshot (IVssBackupComponents::StartSnapshotSet: 0x80042316: Another shadow copy creation is already in progress. Wait a few moments and try again.)
VSS::Perform: Failed to perform VSS snapshot.
Failed to perform VSS snapshot on volume [C:\], retrying soon [1 / 5]...
Failed to perform VSS snapshot on volume [D:\], retrying soon [1 / 5]...

Cause

• The Windows Volume Shadow Copy Service (VSS) architecture allows only one shadow copy creation process at a time across the entire system framework.
• Snapshot Collision (Error Code 0x80042316): This error occurs when Comet Backup attempts to create a filesystem snapshot while another process is already holding or creating a Windows shadow copy.
• Overlapping Backup Schedules: Another Comet Backup job or third-party backup software (e.g., Windows Server Backup, Veeam, Hyper-V host checkpoints) started at or around the exact same timestamp.

Resolution

Check Windows Event Logs for Conflicts:

• Open Event Viewer (eventvwr.msc) on the target machine (CMS-HBT).

• Go to Windows Logs > Application and Windows Logs > System.

• Look for events from sources VSS, VolSnap, or third-party backup services matching the exact timestamp of the backup warnings to identify the conflicting process.

Stagger Backup Schedules:

• Ensure that multiple Protected Items or backup tasks on the same machine are not scheduled to start simultaneously.

• Adjust schedule times so jobs run sequentially with enough buffer time between them.

Check and Reset Stuck VSS Writers:

• Open an elevated Command Prompt (cmd as Administrator) and run:

  C:\> vssadmin list writers

• Verify if any VSS writer is listed in a Failed or Waiting for completion state.

• Restart the Volume Shadow Copy service to clear temporary locks if needed:

  C:\> net stop vss

  C:\> net start vss

• For further VSS diagnostic steps, please refer to the Comet Backup VSS Troubleshooting Guide.