Hello James Snedeker,
After reviewing your post, it sounds like you want to move a file to another disk. I would recommend that you read this article, it may be able to help the issue.
iMovie: How to Save Projects to Another Hard Disk
To copy an iMovie project to another disk:
1. Quit iMovie if it is open.
2. Locate the project folder in the Finder.
3. Drag the project folder to the other disk.
Note: You must move the complete project folder, intact, to the other disk in order to successfully copy the project. The project folder has the same name as the project listed in the iMovie window. This folder includes the iMovie project file, as well as a Media folder, which contains all of the clips associated with this project. If you don't copy all of these items, the project may no longer be readable in iMovie.
Once you have copied the project, try opening it in iMovie to ensure that it copied to the other disk successfully.
Thanks for using Apple Support Communities.
Have a nice day,
Mario