What does this error mean? VSS_E_VOLUME_NOT_SUPPORTED

I’m using UrBackup to do file backups of 2 directories - no image backups. At the beginning of the backup of both directories, I see the messages below in the log. It then seems to carry on and do the file backup properly.

Whatever could it mean?

12/14/16 20:47
Starting incremental file backup…

12/14/16 20:48
backupcom->AddToSnapshotSet(&(Server->ConvertToWchar(wpath)[0]), GUID_NULL, &dir->ref->ssetid) failed. VSS error code VSS_E_VOLUME_NOT_SUPPORTED

12/14/16 20:48
Creating snapshot of “Pictures” failed.

If you google for the error code (VSS_E_VOLUME_NOT_SUPPORTED) you’ll find some things you coult try to fix the error.
It is not specific to UrBackup and returned by Windows.

Im having the same issue, how did you manage to solve it?