Vegas Movie Studio Slideshow Generator Can't Save?

I've never heard of that happening.

Do yourself a favour and make a master folder with all your assets in separate folders (i.e. a folder called SlideShow with sub-folders such as Pictures, Music, Graphics, ProjectFiles, etc.)
When you first start your project, immediately save it (Save As) in the ProjectFiles folder.
What I do is save incrementally. That is, make a few changes, save it under a new name (i.e. SlideShow-01). Make a few more changes, save it as SlideShow-02, etc.
This way, if you do have a problem, loading an older version means that you won't lose too much work.

p.s. Ideally you have all your work on a separate drive and not on drive C.
My computer has 3 drives, drive C for all programs only, drive D for works in progress and drive E for edited programs.

Now I understand.
I use Vegas Pro and Slideshow Generator is specific to your software.
I wish I could be of more help.