I have had a similar problem and cannot explain why it happens. The way I got round it is using Adobe Audition (or similar audio editing program if you dont have it) and imported the original sound track into that and then exported it as an MP3.

I then went back into Premiere Pro and imported the original AVI file, locked the video track, removed the original audio track, imported the new MP3 and placed where the original once laid.

I would then export the whole thing as an AVI and it worked!!

Mark

www.onlinevideosolutions.co.uk