mp2 choking in DVDSP but not in QT?

I've just updated a couple of files for two dvds. The first one worked all fine when I relinked the files, but the second has had some problems. I don't think it is to do with the updating of files, but rather one of the mp2s. When I preview, the second mp2 (a 40min lecture) plays for one second, but then the visual freezes on one frame and starts fading out and then in really quickly. The audio continues playing. When I have tried opening the video file up in Quicktime, it plays fine. DVDSP however can't seem to handle this file. I tried the good old "ignore this problem and build the DVD anyway" but it had an error. Any suggestions as to why it might play fine in quicktime but be rejected by DVDSP? Anyone experienced this kind of problem in the preview? Unfortunately Im thinking my only option is to export another from fcp, but not liking the time it's going to take to do that as it will include 3 hours of rendering as well, and I'm not certain that I won't have the same problem.

Dual 1.8 G5, 1.5G Ram, OS 10.3.9, FCP5, DVDSP4, Compressor 2, QT7

Is the offending file copy protected? If so, there are ways around it that I won't discuss here. You can reach me directly to discuss that topic.

If not, you might try converting the file using Streamclip or DVDxDV.

I ended up exporting the mp2 out of fcp again, and thankfully this time haven't run into this problem. I still haven't reached an answer yet as to why DVDSP was stalling on that video file while QT didn't have any problems with it. I thought DVDSP used QT as its base for playing stuff anyway? Not that I really know how all that works...
Thanks for your help.
Snowy