If you have performed a restore in Spanning Backup for Salesforce, and have received an "operation performed with inactive user [SFUserId] as owner of account", then the owner of the record that you are trying to restore is no longer active in your organization, and you will need to update your data before the restore can be performed.
If this occurs, you can overwrite the 'OwnerID' field for the objects that your are trying to restore during the restore process with the Salesforce ID of another active user in your organization. This way, when Spanning restores your selected records, the 'OwnerID' field referencing the user that no longer exists will be replaced with the ID of an active user.
For more information about how to overwrite field values during a restore process, please see this Knowledge Base article.
Alternatively, you can reactivate the user account with the ID in question in order to complete the restore action. Or, you can export the record, modify the owner ID in the CSV file and use the Salesforce data loader to import the object.