From Millénaire Wiki

Millenaire won't work and someone linked me to this page?![edit]

Follow the below directions:[edit]

Take your world files and copy them to the desktop.

Delete your entire .minecraft folder.

Delete your Minecraft.exe file.

Uninstall all versions of Java you have installed.

Install only the newest version of Java.

Install a new Minecraft.exe file.

Run Minecraft.exe, close.

Install Millenaire.

Move your world files back.

Run Minecraft and try it now.