Most likely there is still something in the system using VSS besides our software when you run it by schedule. You can try shifting schedule for that plan to non-working hours.

Another possible reason is that previous VSS snapshot has not completed properly and is still running. Try to restart the Volume Shadow Copy service. You can do this by going to Start > Control Panel > Administrative Tools > Services: find Volume Shadow Copy and right click and select Restart.

Event logs could also tell more about issues like that.

In addition I can also suggest to enable "Use System VSS provider" option for that plan.

I'm seeing this a lot too these days ... on machines where CBB is the only backup operation on those systems. the backups are scheduled after work hours. Some machines run Win7 some run Win10.. just today was 6 machines throwing this error... so in CBB MBS I'll manually run the job and it will run/finish successfully.. This problem has been going on for a couple of months only.

As with any similar situation, I can suggest to update the software to the latest version, make sure "Use System VSS provider" option is enabled, and in your case you can try to set schedule to the time when you run the plan manually, since something else in the system might be using VSS.

An old topic, but today I had also this problem at one of my customers. The reason was, that my customer had enabled versioning and at the time, when the backup should be executed, the volume shadow copy was running to remove old versions of files. That was the reason for the error.

Thanks for this info! Yes, indeed, native scheduled VSS snapshots may cause this problem.