DVD Movies Freeze After ~25 Minutes

I have used both Cyberlink Power DVD v7 and VLC Media Player v 0.8.6i under

Vista Home Premium SP3 on one box and the same players on another box with

XP Pro SP2. The results are approximately the same.

With the VLC Player I have changed the output module to every selection on

the menu: DirectX, Open GL, etc.

Both systems have 2GB of RAM, The Vista system has an AMD 5000 64x dual

processor and built in 6200 graphics. The XP system has an Intel 2180 cpu

and 8600GTS graphics.

Some movies play full length, others will freeze after about 25 minutes.

Restarting the player does not help nor does rebooting the box.

Any idea what the problem might be and how I can fix it?

Thank you.

Mike