"The attachment could not be opened" message is logged at ERROR level in the 'ExchangeConnector.WindowsService.Host.log' file after running a Schedule archive on one or multiple users' mailboxes. The Journal folder is also not visible from Outlook Web Access (standard).
Exchange Web Service cannot server the requested item to ZyLAB Exchange Connector. This is because Segmentation Journaling has been discontinued since Exchange 2010.
It is safe not to Archive the Journal folder within the users mailboxes as Journaling in Exchange 2010 and 2013 should be set within Microsoft recommendations, either using Standard or Premium Journaling.
In the Schedule configuration page from the ZyLAB Exchange Connector webGUI, untick the Journal folder.
Discontinued features and changes in Outlook 2013