There are at least two problems here
• iTunes can not find Your file - I don't know why. Does it play in iTunes
• To use iTune audio in Movie projects aimed to a DVD - THEN You have to do it in another way due to DRM-Copy protection. So even if You get audio over - the resulting DVD will be silent.
• in iTune collect needed audio into a new PlayList
• Burn this out as an Audio-CD and as .aiff - NOT .mp3
• Use the files on this CD in Your Movie project - iMovie or FinalCut - will work
• Now do not use "Share to iDVD" - but "Share to Media Browser" and as Large (not HD or other resolution)
And DVD made from iDVD will play all audio OK.
Yours Bengt W