Sorry for late reply, fred666.
I visited the drive maker’s web site, but no firmware update is available.
I also tried the custom firmware, but the updater does not support USB connected drives.
Atter try and error, I found a fact that I can play an encrypted disc when I run mplayer command immediatly after inserting the disc.
For more inspection, I found that when an encrypted DVD disc is inserted, “udev-worker” process is locking the disc access. Other type of disc (i.e. non encrypted DVD ) is not locked by this process. I think that it seems to be a cause of this error.
But it seems not to be a practical solution that I shutdown all the udev process. (It is impossible, I think.)
Any solutions?
Thank you.