BTC 1008 "sometimes" cann not read

I have had this drive for many months now and am very happy about it. Yesterday I tried to read some dvd (chinese TV episodes) and 2 of 10 disc can not be read by my BTC. I tried these 2 dvd on my regular dvd player and it plays fine. I also try them on my notebook’s dvd player and they play fine too!. But when I tried them on my desktop’s BTC, the drive keep spinning anc can not read the disc. After I eject the disc, my BTC can read other episode fine without any problem. It only has this problem with these particular 2 disc out of 10, and these 2 disc are fine for other dvd player and readers.

Does anyone have the same problem? How can I fix this probelm?

Thanks
Albert