iMovie on iPad mini says "Move playhead to wider audio section!?"

My iPad mini has iOS 6.1.3, And I'm using iMovie version 1.4.2. Anyway, when I was editing a movie, I try to add a sound effect to the movie, but it said "Move playhead to a wider audio section", And I was confused, because when I tried to add the sound effect, there were no sound effects there. It said there were too many sound effects there, when there were no sound effects there. I have no idea why that happened, because no sound effects were there. Please help.