Hi, Lightbug 1,
Try booting up in Safe Mode and, after everything loads, immediately reboot in normal mode. Don't try to open iMovie in Safe Mode because it will not do so. After rebooting in normal mode, see if you can share out.
If Safe Mode doesn't solve it, try redownloading iMovie. To update/redownload iMovie 10, drag your
iMovie 10 app from the Applications folder into the trash, but do not empty the trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash and return it to the Applications folder.
If still not working, and if you haven't already tested with another project, try creating a new project and see if you can share out with different media and also with the same media that you are working with now.
Another thing that you can try is to create a new user account (System Preferences/Users and Groups) and see if iMovie will share out in the new user account.
-- Rich