problems with clondvd

[scottiedog]

hi all, I hope someone can help me
I have recently brought a pioneer -r burner. I have been using dvd decrypt and clonedvd. My problem is that when i try to back up, (in particular harry potter chamber of secrets and men in black 2) towards the end of the film the picture and sound starts freezing and or the film then starts to skip through the chapters.
when using clonedvd i have copied film and extras. I have converted my hard drive file system to ntfs as i had same problem as highlighted in another thread and thought that, that might be the problem.
I thought it might be the media i was using but i have copied other films successfully using the same discs.
The only thing that i haven't done with my limited knowledge is to re-decrypt the films in question, as they were put on my hard drive before i changed from fat32 to ntfs.
Any ideas would be greatly appreciated as my house has loads of brand new harry potter coasters.
thanks in anticipation