The Trash in iMovie shows that it is not empty after deleting some clips and emptying iMovie's Trash.
Solution
On some newer computers, iMovie 1.0.x may report that there are clips in iMovie's Trash, although the clips have actually been deleted. This issue is cosmetic, and does not affect your ability to use the application. iMovie 2.0 and later addresses this issue.
For information about the latest version of iMovie, visit: http://www.apple.com/imovie/ .