It's a 38 minute movie of many home movie edited scenes from a nice little Panasonic HD camera.  The scenes all play in the project, but when I save the movie, at about minute 30, every other scene is a black video but the audio is there!  Any ideas as to why? and how I can fix it?  I'm trying to get this done for the family for Christmas... something that should have been straightforward after all the time in editing!  Thanks in advance for your help.