I updated to DVDFab 5050 and found that whenever I did anything which involved the preview player, DVDFab crashes with the screen to send in details of the crash (which I did). eg. If you switch to the Main Movie option, the screen comes up with a black screen on the preview. Over the next few seconds it starts to show information - title number, chapter number but then just as a picture should appear it crashes.
After much messing about - uninstalling and re-installing, I have gone back to version 5030 and everything is fine. Looks like a bug with the direct show viewer.