Check if there is another "save" folder inside the save folder you copied them into, that happened once to me. Instead of copying the files into the new folder I accidentally copied the folder into the folder, and thus it didn't work.
If not, did you only copy the file? You need to copy everything in the previous save folder and paste it into the new build's save folder.
Also, did you unrar/unzip the files. Saving doesn't work if you don't unrar/unzip the game.