Can't read some DVD - QSI SBW 241



I have a combo QSI SBW 241 on W2K and I have powerDVD application and I usually watch DVDs… But it does not read some DVDs that I can watch it on my pioneer DVD player at home…

QSI SBW 241 is free region, it should not be related with region code… Anyone knows what should be the problem? and there is a way to solve it via a software?