I had the same problem with ARCserve2000 and brick-level backups. Solution: You’ll need to select each individual item for Backup. That is, instead of clicking on "My Computer" and ARCserve automatically selecting all items for/to backup, you'll need to select each item individually (C:, D: drives, registry, system state, Exchange Server, Exchange Server-Brick Level). By selecting each individual item, you should notice that "My Computer" selection box is now half shaded, instead of full shaded. This method will make ARCserve think that you are not running a full/complete backup, thus enabling you to backup your entire server, including Exchange Server Brick-Level backups. ARCserve is aware of the problem, but have not commented on a fix.
-Manny