I see this often and try using Java 6. It actually fixed it for me.
if that doesn't work. i usually get it to work with gulliver forge. it installs the mod for you. MAKE SURE you are using the correct forge version for the mod.
There are 2 different versions of forge the main post is talking about.
one is for 1.6.4 and the other is for 1.5.2