I lost a HUGE save the same way, before i realized that the stupid directory i stupidly installed the game to was stupid read-only. The game itself gave me no indication what the problem was; it just made the "doonk" cannot do sound when i tried to select a save file. I made the folder writable - but then I ended up just extracting to my desktop to guarantee write ability.
However, alas, the Book had crumbled to dust before I figured it out.
Still, I hope this helps.