Voiceover in iMovie 11 not playing - yellow exclamation mark and yield sign instead

Hi,

A while back I recorded a voiceover through iMovie 11 and saved it with my video clips in an iMovie project. Today when I was editing my project, I moved the voiceover around here and there, copied it, deleted it, and tried pasting it in another place in my project. When doing that, although the voiceover got pasted, it no longer worked. Instead a yellow yield sign with an exclamation mark appears on the purple voiceover track and when I click to play it, no sound comes out.

What can I do to make this voiceover work again? I think I should re-locate the exact location of this voiceover file on my mac so that perhaps iMovie isn't confused about where it's at, perhaps then it will play again.

Please help!!!! responses much appreciated.