What do you mean they don't work anymore? They aren't listed in the Load screen? Or you can load them, but the game crashes?
If they are invisible: move your old saves somewhere else; launch the game; save in the same slots where your old files were supposed to be -> the game will create files called file1.rpgsave, file2.rpgsave, file3.rpgsave, or whatever; finally move back your old files into the www\save folder, and overwrite the ones the game has just created.