Trying to make a disc.img from an iMovie project get the mssage that some of the audio clips are not available. The clips still show as green bars in the project but do not play.

I successfully made a disc.img and then burned a DVD of the project but found an error in a title. Went back to the project, corrected the error, and tried to create a new disc.img but got the message that some of the audio tracks were unavailable. They still show as green bars in the project but do not play. Tried deleting and reinstalling them with no success. They do play in iTunes and in the iMovie editing pane

Thank you