Like the title says. Updated the pack.json file.
here is minecraft.txt
D:\Games\Minecraft\FTB\MinecraftLog.txt: written by FTB Launcher
[12:30:34] [main/INFO]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[12:30:34] [main/ERROR]: Unable to launch
java.lang.ClassNotFoundException: cpw.mods.fml.common.launcher.FMLTweaker
at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.8.0_66]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_66]
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) ~[?:1.8.0_66]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_66]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:106) ~[launchwrapper-1.11.jar:?]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_66]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_66]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_66]
at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_66]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:98) [launchwrapper-1.11.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.11.jar:?]