So just to clarify, both SBS servers have a tape drive installed in them, you take the tape from Server A, put it in Server B and try to restore the data from the backup on to itself?
Is Server B already configured and running as an SBS server?
I'm about to have a play with manually restoring an existing SBS server backup to a new system, so I'll see what I find, and if I see anything similar when I try.
Will report back
Keith