gconcat/gbde DVD encryption problem

[RW]

A couple of years ago, I created some DVDs encrypted with gdbe. I used 2 
concatenated,  file-backed md devices (to avoid the 2GB dvd file limit) and 
burned them to dvd. The resulting DVD was accessed like this:

----------------------------------------------------------
mount  /dvdrw

mdconfig -a -t vnode -f /dvdrw/d1 -u 31
mdconfig -a -t vnode -f /dvdrw/d2 -u 32

gconcat create datadvd /dev/md31 /dev/md32

gbde attach /dev/concat/datadvd

mount -o ro /dev/concat/datadvd.bde  /mnt/dvd
----------------------------------------------------------

The technique worked fine in  February 2005, with whatever was the latest 
release, I haven't used the technique since then until a few days ago,  but 
now I'm having a problem with FreeBSD 6.1. After the mdconfig I get "WARNING: 
opening backing store: /dvdrw/d1 readonly", which I doubt is the problem. The 
failure occurs here:

# gbde attach /dev/concat/datadvd
Enter passphrase:
gbde: Attach to concat/datadvd failed: could not access consumer


The same problem exists on a newly created disk, so it probably not 
corruption. And if I copy the two file to hard disk it works.  It just seems 
to be a problem when they are on the DVD.

Any ideas on how to fix this. I'm not particularly bothered about the existing 
disks, but I'd like to create some new ones.