Hi,
Those are temporary files that iMovie places on your desktop to assist it in exporting the movie. They have a tiny file size, as you can see, and they cannot be played. When the movie finishes exporting, the temporary files will shortly disappear and be replaced by the fully exported movie. So, perhaps you are not waiting long enough for the movie to finish exporting.
If the export actually is stuck, sometimes deleting/resetting preferences can cure it. To delete/reset preferences close and then open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new empty library. Reopen your old library to get back to your projects. Now see if you can export. Possibly you may need to reboot to set the changes. Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.
Another thing you can try is to create a new project and see if you can export from there.
-- Rich
