At the end of every level, is a 'boss puzzle', a puzzle that is more challenging than the ones you have currently been solving. This puzzle must be completed to capture the trickster, put it back in the box and go to the next level. Some images were difficult to see, especially the Find and Fill puzzles, where the shapes were impossibly small and dark. I liked the background music. Not the toe-tapping variety but not annoying either.
System requirements are very reasonable.
I couldn't find any rhyme or reason for this, nor a patch. If this happens to you, I recommend saving just before you slide the last piece into place, then exiting the puzzle and then going back in to finish the puzzle. I didn't have any problems when I did this. Pandora's Box is a good game. You could even call it a 'nice' game.