With Powerpoint 2010 ppta goes FLUSH

I am finishing up a project that I started more than a year ago (the client flaked, then panicked).
I started it in Powerpoint 2007 and am now finishing it in 2007 because most of the time when I opened it in Powerpoint 2010 all the attached sound and most of the synchronization just disappeared. I keep a Windows Explorer window open when I'm working in Articulate and I could see the ppta file suddenly and inexplicably collapse from 100 megs down to 12k.

I cannot find a pattern. Sometimes it happens the instant I open the file. Another times the file opened fine, I previewed some slides, I opened "Import Audio" and all the sound files were there, then I opened the "Audio Editor," which appeared to load very very quickly, but when I expanded it to full screen there was not audio (I checked in the Explorer window and the ppta file had collapsed). Sometimes, though it is rare, everything goes fine. This has happened dozens of times with many different files and projects.

As you can imagine, I'm pretty skiddish about doing anything important in PPT 2010. I'd love to be able to use the features in PPT 2010, but I have never been willing to actually create and work on a project in 2010 because of this problem.

I suppose THAT could be the problem. There is something about files created in PPT 2007 (or the Presenter plugin for it) that PPT 2010 (or the Presenter plugin for it) does not like, but that's just a guess.

Does anyone have any idea what is going on? Am I doing something wrong?

Thanks, JP