For some reason iMovie is not letting me import some of my files. They are saved as a .mp4 file but when I got to import them it will not let me highlight them. I have other files saved as .mp4 and it will let me upload them. What is the issue? It seems to be all the files over 5 minutes long it won't let me import them, and all the files under 5 minutes it will. Here is a screenshot of an example: