Update: The project is copied. After reading that Project Manager will not trim long GOP footage, I tried the option for copy entire project rather than trimmed project. It worked fine. Just a little bigger than I would have liked. I think some of the .mp4 files shot with a DSLR are long GOP. I wish Premiere Pro would have just given me a warning rather than a crash-o-rama, but whatever. It's done. I can move on.
Thanks everyone for trying to help.
- Carolyn