WinDVD 5 and 6 freeze in the middle of a movie

Just in WinDVD and not in any other player will the movie freeze (audio and video stop) and the computer will lock up and i am forced to reboot. this doesn't happen when playing a movie off the hard drive but only during DVD disc playback. usually it occurs towards the beginning of the movie or not long after i have started, if i don't start at the beginning. sometimes just the video will become garbled, a weird green block pattern seems to cover the normal video, very ugly. These symptoms do not occur every time i play a movie yet it can occur with either of my two DVD drives.

anybody else having problems with WinDVD??
any suggestions on what could cause this??