I have found a solution. I'm surprised that Apple let this happen without immediate posting on the Forum here.
You can use Update and Projects, but only one at a time.
A. I Quit iMovie10. Then I trashed the files that all of you have been trashing...the "UpdatedtoiMovie10" files in iMovie Events and iMovie Projects. I also trashed the iMovieLibrary and iMovieTheater files.
B. What I've done is create to subdirectories, one called Events and the other called Projects and put them on my desktop.
C. Then I moved all my iMovie 9.0.9 events (don't worry you won't lose them) into Events and all my iMovie 9.0.9 projects into Projects.
D. Then I moved ONE project and ONE event back into the iMovie Project and Event subdirectories.
E. Next, I reopened iMovie10 and selected Update Events and Projects. The project and events were brought in for that one project.
F. Then I quit iMovie 10 and repeated A through E for the next project.
What won't be accurate will be the listing of which projects you updated. But who cares. Most people won't want ot move all their projects over anyway. The actual movie projects will be in the iMovie Project timeline as separate editable projects.
I am sure Apple will have a work around, because this is a pain in the rear if you have many you want to bring over.