Warning errors after upgrading to new release


I have just upgraded to release on some Windows 10 machines and started to receive Warning error messages due to open files that cannot be backed up. These files correspond to *.pst files from Outlook and in previous release did not happen.

Is there another new release in other software necessary?

Thanks and Best Regards,



This setting controls the usage of snapshots, which allows Duplicati to backup files that are locked by other programs.

and this is how it has been for a very long time. What was the setting for this, before and now?

Hello ts678,

Thanks for your reply, the snapshot policy has been set to Auto before and after the upgrade. I have observed though that in some cases it works with the setting in On and sometimes in Auto. But in this case, neither.

So old release was intermittent, and new one is solid not working? For me, is doing fine.

Because I don’t have a .pst file handy, I tested Duplicati’s lock_v2 file. That might be in folder


however note Windows VSS needs Administrator privilege, so either SYSTEM or UAC elevation.

Testing as an elevated admin, I could backup lock file fine at Auto or On, and Off gives Warning.
I usually use Required because I know I’m backing up locked files. Worked fine before and now.

Some more tests on your end is probably needed. It’s especially odd multiple systems are failing.
If the previous release was intermittently failing though, that’s something needing an explanation.
Simplest one would be that Outlook isn’t always up, but I don’t know if that could be the situation.

I don’t see anything in About → Changelog recently, and I don’t find any GitHub Issues on this.
You can look too if you like. One other thing to study is in a Command Prompt (Admin), look at

vssadmin list shadows to see if there’s a new shadow during backup. That’s VSS at work.
vssadmin (Microsoft) has some other variations to try. Default storage has seemed low to me.

On a system with a hard drive, you can usually tell when VSS is starting, as other things stop.

The difference between these settings is a bit non-intuitive, so here is a description:

  • off: Snapshots are not used
  • auto: Snapshots are activated if permissions allow it, otherwise nothing happens (aka “silent on”)
  • on: Snapshots are activated and will emit a warning if the setup fails
  • required: Snapshots are activated and the backup will abort if snapshots cannot be set up