PowerDVD6 crashes seconds after playing DVDs from DVDdrive

[Gwion]

I am using PowerDVD 6 and so far had no problem with it. It plays avi,
and mpg and if you chose the option "open media file" it shows the files in video-Ts and plays selected parts.
However when I chose the option "play DVD from harddrive" it starts playing (usually the logo) but when the menue appears it crashes. I have tried it with PAL and NTSC, no difference.
When I tried to play a vob with Windows Media Player (9), it tells me
Error: ClassFactory can not supply requested class.

The DVD drive is a NEC DVD-RW 1300a.
PowerDVD 6
OS: WinXP

I don't think that the DVD is the problem (since I tested with severals). Any ideas what causes the crash and how to fix it?

[SLK001]

The problem is in the encoding of the DVD. A lot of DVDs have errors the are ignored by a standalone player, but are "played" by a software player - thus, the program crashes.

[Gwion]

Um, no I don't think that's the DVD. It wouldn't have played the vob otherwise.
I installed PowerDVD 5 and presto, now it works smooth.

Thanks for reading anyway.