GOP Timecode/ Sync errors

[BCAESE]

When using DVDLab I noticed the GOP timecode fix feature.

I have done may movies with DVDLab but occasionally I get sync problem when authouring.

This usually happens with movies that are converted from PAL to NTSC.

Seeing that it doesn't happen all the time I was wandering if it is because the video file has GOP timecode errors

If this was the case do I fix the video in DVDlab in the PAL state or after I have converted it to NTSC

Does this elimate sync errors when authouring

My encoded NTSC file usually plays fine in POWERDVD, but when authoured to VOB file in DVDLab it gradually falls out of sync as the movie progresses.

Why doesn't POWERDVD recognize GOP timecode errors on playback of files

Is the GOP timecode the cause of the gradual sync problem

[BCAESE]

Answers? Anyone