IMovie '11 stopped playing some of my audio sound effects.

Question

I completed a project in iMovie '11 yesterday and today opened it to fine tune the musical scoring. I'm using a 2011 MacBook Air 13 in. Yesterday all the background audio files I had placed, as well as the pinned audio (that iMovie calls "sound effects") worked fine. Today the first few will play and the rest are muted. Also, if I should add a sound effect or music file to the timeline, it appears normally, but remains mute. Nothing comes out of the speakers. The sound file will play fine in the Audio window. Selecting it and then hitting the play button (or double-clicking it) will cause it to play normally. But when I drag the file over to the timeline and drop it on a clip, it attaches normally and looks fine. But when I play the video, there is no sound. Now here's the strange thing. If I copy one of the audio files that DOES play and then paste it back into the timeline, it will not play. It's the same file, but at one point it plays and at another it does not. This problem does not occur with background audio files. If I take the same file that will not play as an attached "sound effect" and paste it into the background as a big green background audio file, it will play.
So, what's going on? I don't recall doing anything since yesterday (when everything worked fine) that might have caused this aberrant behavior. Have you ever encountered a problem like this? Any idea about what I can do to correct this? Thank you for your swift reply. I'm facing an urgent deadline.

Answer 1

The "yellow caution badge" that Peter refers to indicates that iMovie can't locate the clip, whether it be video or audio. The "badge" is in the shape of a yellow triangle enclosing an exclamation mark - see this picture:
One tip that may help is to delete iMovie's preference file. That file can become corrupted under certain circumstances, such as when iMovie quits unexpectedly or is Force Quit.
The file is located in your User (Home) folder Library/Preferences and, for iMovie '11, is named "com.apple.iMovieApp.plist".
Close iMovie, then drag the .plist file to the Trash. When opened, iMovie will create a fresh .plist file with the default settings, which you can change if desired in iMovie's menu item iMovie>Preferences.
Deleting the file will not harm your existing Events or Projects, but may fix iMovie's abnormal behaviour.
NOTE: I have seen similar behaviour myself, as you and Peter describe (but not as serious - it was on a test project). My fix was to check each and every audio track and switch Ducking OFF and ON (or ON and OFF depending on its setting). The disappearing audio suddenly re-appeared on the problem track. But it may have been coincidental, as I was playing around generally - perhaps something else I did triggered it.
John