DVD Studio Project PAL to NTSC

Hi,
I have a DVD Studio Pro PAL project with subtitles and many other things and I need to have it in NTSC as well. I've tried to change the general tag to NTSC and to create NTSC clips but the DVD created is not readble by the computer...
What can I do?
Thanks

Convert your video to NTSC first, next you will have to redo your subtiles (and your other media), then encode this to m2v and use that in a new project. Audio is the same in both formats.

Cheers
Alexander