Hello Burney,
I understand you are getting an error when trying to perform a Back-up on Unity version 7.x, which does not allow you to complete it to 100%.
1- Do you have any ES (Engineering Special) or SUW (Server Update Wizard) installed in the Unity system?
2- Does the error appear only for manual backups or does it also appear for scheduled backups?
3-Do you get any additional information on the System and Application logs on the event viewer?
4- Have you run the DBWalker to check your database health?
5- Do the Unity accounts have the proper permissions over the mailboxes that contain the messages you want to backup?
6- Do the Unity accounts have Exchange the right memberships (i.e Ex2k10 Organization Management)?
Best Regards,
David Peck