After seeing this thread, I just ran through almost all of my Warner HD-DVDs (about 15 in total) on my Toshiba A30. I started each one up, ran through the menus to check/change the audio options, played the first chapter and then either fast forwarded or skipped to the middle chapter or the 50 min mark, and then either played or FFWD through to 1h15m or so, and then tested a few random sections of the movie.
Fortunately, they all seemed to work. I did notice that on most of them there was a film on the inside of the plastic case - even on packages that were still factory sealed.
I had a problem with the player about a year ago - I had purchased a few HD-DVDs and first one of the new ones wouldn't play; then the others; then even many of the older ones that I had watched before stopped working properly. Some wouldn't boot up, others would freeze up. I was ready to buy a new player.
Coincidentally, around the same time my BR player started glitching, and Samsung told me to manually update the firmware. I did, and it fixed the problem... so I did the same on the A30... and it solved all my problems. It was weird, because I hadn't done a firmware update since some of the older discs played successfully, but playing the newer one seemed to screw it up for all future discs.