I'm making a mod for Minecraft, but the test button won't work. Here is what it does when I click it:
Jun 01, 2014 8:43:20 AM net.minecraft.launchwrapper.LogWrapper log
INFO: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
Jun 01, 2014 8:43:21 AM net.minecraft.launchwrapper.LogWrapper log
SEVERE: Unable to launch
java.lang.ClassNotFoundException: cpw.mods.fml.common.launcher.FMLTweaker
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:102)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:94)
at net.minecraft.launchwrapper.Launch.main(Launch.java:27)