I am using the X Mod Pack 2.0.1 (http://xmodpack.weebly.com/) which works just fine but as soon as I install Millénaire 3.3.2 (http://millenaire.org/) the game crashes on startup.
The Forge version in use is the one that comes with the X Mod Pack (minecraftforge-universal-1.4.6-6.5.0.472.zip)
ForgeModLoader-client-0: http://pastebin.com/rNZ272FJ