This happened to me too.
I had a backup though and found a way that works. (My "fix" opens them ok anyway. I haven't done any editing with them yet.)
I think it is related to moving your project. In my case I just got a new USB memory stick and it uses a new drive letter (H: instead of I: ). The problem showed up when I moved my stuff from I: to H:. I do all of my work (C++, C#, Word, Silverlight) on my memory stick so I am not tied to any particular computer.
Before opening your project, with the november version, edit your *.dzprj files and make sure they use the correct drive letter.
what seems to be happening is that the new release changes <SourceDirectory> and <TreeDirectory> like it should but it deletes the <ImageList>.