After much looping around when entering the information for my AMVs, I realized that checking the boxes next to the music and video footage is a bad thing...
At first glance, it looks like you need to check the box before pressing the continue button to add the song/video to the database entry. However, checking the box deletes the song/video from your entry whether you press the continue or the delete button. There should be a little note somewhere that says "Do not check the box unless you are deleting the item"... or something like that...

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