osnapit:
Download the following files:
http://files.minecraftforge.net/fmllibs/argo-2.25.jar
http://files.minecraftforge.net/fmllibs/guava-12.0.1.jar
http://files.minecraftforge.net/fmllibs/asm-all-4.0.jar
http://files.minecraftforge.net/fmllibs/bcprov-jdk15on-147.jar
Once downloaded, move them to .minecraft/libs/