Hi, sheepshoop1,
You might try redownloading iMovie, as that procedure has sometimes cured insufficient disk space errors in cases where the disk space is in fact sufficient. .
To redownload iMovie, move the iMovie 10 app from your Applications folder to the trash, but don't empty the trash. (Don't touch the iMovie Library itself, that is in the Movies folder. It is separate from the iMovie app. If you delete the library you will be deleting all of your projects.) Once you have put your iMovie app in the trash, sign in at the online app store and click on your name at the bottom of the app store sidebar. That will reveal your purchases, including iMovie 10. Redownload iMovie from there. After you have successfully redownloaded and everything works fine, you can empty the trash of your old app. If for some reason you are not able to redownload, then move the iMovie app from the trash back into the Applications folder.
Once you have redownloaded, see if you can import media into iMovie.
-- Rich