ArcServe 6.5 @ Exchange 5.5

I use ArcServe 6.5 for backup of my Exchange server and it works fine, but I am faced with a serious problem. For the needs of client I have to set up a bricks level backup of individual mailboxes. At first, a complete bricks level backup was required, but now, since this company is quite big, a partial backup will be performed. There is just one problem: in ArcServe Backup, I cannot expand Bricks Level view to select those mailboxes. I don’t know why, but system acts as though as there are no mailboxes, altough this view worked just fine a couple of weeks ago. I saw it work myself. I searched everywhere for answer, but without success. Does anybody else have an idea how to resolve that?