iMovie audio cuts out 15 seconds in

Hi - I'm on deadline for a project and I can't seem to figure this out after much troubleshooting - *please help!*.

I'm using iMovie '11 (version 9.0.5) on a MacBookPro (2012) with OSX 10.7.5.

I've imported video and then detached the video's audio and deleted it. I then imported audio from iTunes and dragged and dropped it into my project timeline. It runs successfully for 15 seconds, and even though the file seems to continue for the duration of the video, the wavelength (and thus audio) cuts out after 15 seconds and is silent for the rest of the video. When I play this same file in iTunes it plays through perfectly for almost an hour. I've deleted the audio from the timeline and reimported it twice and have checked and don't see any muting occurring, so I'm not sure what is going on.

Also, I'm not sure if this means anything, but the audio file changes from green to purple once I move it to begin at the beginning of the video (when I drag and drop from iTunes window in iMovie, it automatically places the audio at the beginning where I have a Title clip and transition. I want the audio to begin at the beginning of the actual video (and continue playing throughout video). Does the green to purple auto-change matter (why does it do that? what does the color change mean?).

Please help. Thank you!