What happened to DVD writing?

[Warren Block]

Recording data DVDs worked a few weeks/months ago on this system with a 
PATA Lite-On DVD recorder:

FreeBSD lightning 7.2-STABLE FreeBSD 7.2-STABLE #0: Sun Sep 20 07:25:58 
MDT 2009      root at lightning:/usr/obj/usr/src/sys/LIGHTNING  i386

Now growisofs starts, but appears to never manage to write to the DVD. 
It's a DVD-R, one from the same batch that has worked before:

   0.77% done, estimate finish Sun Sep 20 07:55:57 2009

and there it stops.  Rebooting is needed, and the machine can't quite 
bring itself to shut down after syncing buffers.  /var/log/messages:

Sep 20 07:42:44 lightning kernel: acd0: FAILURE - READ_BUFFER ILLEGAL REQUEST as c=0x24 ascq=0x00
Sep 20 07:42:46 lightning kernel: acd0: FAILURE - MODE_SELECT_BIG ILLEGAL REQUEST asc=0x24 ascq=0x00
Sep 20 07:42:56 lightning kernel: acd0: FAILURE - READ_TOC ILLEGAL REQUEST asc=0x24 ascq=0x00
Sep 20 07:43:25 lightning kernel: acd0: WARNING - TEST_UNIT_READY taskqueue time out - completing request directly
Sep 20 07:43:36 lightning kernel: acd0: WARNING - TEST_UNIT_READY freeing taskqueue zombie request
Sep 20 07:45:26 lightning kernel: acd0: WARNING - PREVENT_ALLOW taskqueue timeout - completing request directly
Sep 20 07:45:26 lightning kernel: acd0: WARNING - PREVENT_ALLOW freeing taskqueue zombie request

-Warren Block * Rapid City, South Dakota USA