The first thing to do is make sure you have the same version of the game as the saved game you want to download.
Unless you are playing the disc version of the game, the saves at nicouzouf are probably not going to work with your game.
The older download from GOG was configured using ScummVM. If a game is played in ScummVM, saves will not be compatible with the original disc version of the game. They won't even be compatible with saves made with a different version of ScummVM.
The current version of BS2 at GOG is a "remastered" version. Saves from that version won't be compatible with saves from the original game. It's a different game.
If you are playing the "Remastered" version of BS2, you will have to find saves that were made with the "Remastered" version of BS2. Otherwise you are wasting your time.
If you are using a walkthrough made for the original game on CD, and you're playing the "Remastered" version, you need to look for a walkthrough made using the "Remastered" version. Sometimes "Remastered" just means changes to graphics and/or sound. But "Remastered" can also mean puzzles are removed, puzzles are added, whole chapters are removed or added, etc. The game can be very different to the original.