Okay, figured it out, has to do with frame sync. When I first started trying to import the video I tried to use Roxio Media Import. However it has a nasty quirk that if it comes across a section of an input stream that has no sync it STOPS capturing the video. Since I had a bunch of tapes (about 20 out of 30) that had breaks, it meant having to restart the capture over and over. So I gave up on it and switched to AVS Video Recorder, which will keep recoding until there is no signal (which is different than just no sync). Then when I split up the captured video into individual movies, in some cases I left "video" in the mpg that had no picture, and it showed up as basically blue filler or jitter. It seems THAT is what MyDVD did not like. Once I took these bad frames off the front of the clip they worked fine and I have been able to successfully create the DVDs for the 2 projects that were failing.
Lesson learned, make sure all your video clips are "clean" before you try to encode them.
To answer your questions though, they all did play by themselves in MyDVD Preview mode. I think I did try one in VideoWave, and I think it played, not positive. I am sure I'll run into this probelm again (like I said, I have about 25 DVDs to make), so I'll try VideoWave and see if it picks up the problem.