iMovie 10 will only update projects and events from iMovie versions beginning with iMovie 7. It cannot update projects and events from iMovie 6 and earlier. I suspect that you might have iMovie 6 since your movie was made in year 2007.
If you have an older Mac that still runs iMovie 6, you can open the project there and either add your updated edits in iMovie 6 and export, or export the project as a standalone movie in its present form and import that into iMovie 10 as one long clip. Editing in iMovie 10 will be somewhat limited, but you will be able to split clips, delete clips, trim, add titles and add effects like picture in picture.
If you don't have the iMovie 6 app, you can control click on the project's icon, and click on Show Package Contents/Media and access the project's media there. You then could copy (not move) the media to your desktop and import into an iMovie 10 project for re-editing.
Also, after clicking on Show Package Contents you can click on Shared/iDVD and you should see a .mov file of the project that you can play with QuickTimePlayer 7. You can then do a screen recording of the movie as it plays, that will give you a movie that you can import into iMovie 10 for editing.
-- Rich