By deleting the ".meta" folder you remove the meta information about the backup
With the "Backup metadata" option checked you will later be able to restore mailboxes from the backup. Otherwise – you will not
Rename the metadata file to its standard name or recreate the metadata files.
Some metadata is stored unencrypted in an encrypted archive
The operation fails because the archive meta information is damaged or missing. Run vault validation to fix the issue
Backup to unmanaged vault fails if the XML file with archive metadata is corrupt
The following conditions are met: