I've been having this same problem... See: https://forums.symantec.com/syment/board/message?board.id=be11dOther&thread.id=2067
Note that for me, encryption works in a B2D folder, and there are fixes on the forums if you are using an LTO drive. My problems are with both of my DLT drives. The last file it tries to back up it crashes on, goes into "communications failure" then "recovered", then "failed". It does not matter what the last file is. (we even set the services on the server to "autorecover" if they stop, and it did not help. I've been working for the last few weeks with support on my problem, with no luck so far. I even tried upgrading to version12 to see if it was fixed, but ran into so many other problems I rolled back to 11d. Awfully frustrating since the only reason we purchased 11d was to do encryption! Everything but seems to work fine for us..