I recently had a problem updating to 1.2.3, so I had to reinstall Minecraft.exe and Minecraft_Server.exe.  Before doing this, I backed up the saves folder from .minecraft and the world folder from my server folder.  I reinstalled the executable files and put the old saves folder in the new .minecraft folder and the old world folder in my server folder, but when I start multiplayer, it loads a brand new world instead of my old saved multiplayer world file.  What am I doing wrong?