Hi, Tadpole66,
First, go to the Finder menu and click on Apple Logo/About this Mac/Storage and confirm that you do in fact have sufficient disk space. You should have about 25GB although iMovie can function at 5 GB.
If you have sufficient disk space, then try redownloading iMovie, that usually solves this issue. 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. Now see if the "not Enough Disk Space" is solved.
-- Rich