I get this error..
Pack: Blast Off! 1.7.10
Setting MinMemory to 256
Setting MaxMemory to 6144
Defaulting PermSize to 256m
[11:42:35] [main/INFO]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[11:42:35] [main/ERROR]: Unable to launch
java.lang.ClassNotFoundException...