Hello
Notification file store notification created by default and also notifications created by you, if file has not been upgraded is due file is corrupted or any entry is worng
Please check if the notifications are set correctly (C:\ProgramData\OmniBack\Config\Server) try to edit it and check for any strange characters. Some times during the installation the notification file gets replaced and the notifications stop working. If this is the case you could set up your notifications again or you could restore the notifications file from a backup and replace it.
Best Regards