[Carl Marten]

You could try using Sorenson Squeze. If you are editing in PPro export the sound and audio seperatly and combine them in squeze (hint it is the best quicktime app). If it is a strait conversion then pump the avi into squeze.

If you realy want to get things working via PPro then export uncompresed audio and video seperatly, then in a new project (uncompresed settings) load your files and then try to export a .mov.

The problem is often partialy compatibly codecs. You need to remove the guess work. (this happens most often with the mp4 codecs, divx, xvid etc or un-specified av combos)

This problem tends to happen on a PC with loads of codecs instaled. Whilst files will play on the actual PC editing and recompressing are a pain.