Comment 5 for bug 430605

Klaus Doblmann wrote: I did not find any apparent reason why some discs fail and some don't.

In my case have found that the media that refuses to mount tends to be newer movie DVDs. Older DVDs, data discs, music CDs are OK for me. I suspect the problem is down to some kind of DRM encryption used by the DVD producers, but I am not sure. These discs used to be supported, is it possible one of Ubuntu's decryption schemes has been removed or broken?

My TS-L632D DVD drive and media are all region 2.

I feel I should also mention that I have had some trouble burning DVDs, that seems to coincide with the not-mounting problem. Maybe other sufferers of this bug could confirm whether they are related.
The default Brasero burning software didn't work (it would claim to work, then spit out an error and an unusable disc at the end of the burning process.) I switched to Gnomebaker for my burning needs and that problem went away. The not-mounting problem persists.

If the not-burning and not-mounting problems are related, perhaps the cause of the problem could be found by examining what resources gnomebaker and Brasero have in common, and what they implement independently.
Whatever the bug is, I suspect it was introduced in about April or May 2009, since that seems to be about the time the problems began.

More information at http://ubuntuforums.org/showthread.php?p=7673049