'persistent' file is exist in 2 folders
1) %appdata%/renpy/lustfuldesire...
2) in your game folder, there is a folder name 'game' in this folder has a folder name 'save' and this save folder has another one persistent file
a file name 'persistent' must be exist in those two folders among all of your save files. You must understand that persistent file ≠ save file and persistent file is a very important file. If you lose this file, your game may occur some bug.