cryptsetup, can't create device from encrypted dvd

[Nomen Nescio]

I tried to make an encrypted dvd this way (using cryptsetup
1.0.3-0ubuntu1)

$ mkisofs -r -J path/to/stuff/  |aespipe -H sha256 -e aes256 -T >foo.iso
[entered passphrase twice]
[waited a while]
[ended up with a 4.2GB foo.iso]

$ dvdrecord -v -dao dev=/dev/dvdrw foo.iso

$ eject
[pushed the button on the drive to suck the dvd back in]

$ sudo cryptsetup -c aes -s 256 -h sha256 create cd /dev/dvdrw
[entered sudo password]
[entered crypto passphrase]
Command failed: device-mapper: reload ioctl failed: Invalid argument

[tried again a few times, with the same result]


Anyone know what I'm doing wrong?