Did you ever get this to work? Does Cubase start other projects normally?
The demo does not have 5588 files associated with it. Maybe 15 to 20 .wav audio files. That’s it.
Hopefully you were able to open one of your projects using CB 8.0.30.
If yes, then my guess is that somehow the demo download was not properly completed. Or maybe it got corrupted somehow during the unzipping process.
If no, are you sure you downloaded the correct demo file for CB Pro 8, not CB Artist 8. Also, are you sure all of the sound content that came with CB Pro 8 was installed too?