This is a known problem and I wish SoFo would fix this. The problem is that Vegas creates OpenDML (AVI version 2.0) compatible files by default and some applications can't handle this but I think its more that just OpenDML. The best workaround I have found is to render without OpenDML but then you are limited to only 2GB files. Not a very good workaround but it’s the only solution as far as I know. The steps on how to do this are outlined in the Vegas Video Tips section of my web site.