[Support] Can't install, gives error

java.lang.NoClassDefFoundError: forge/IUseItemFirst
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
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 java.lang.ClassLoader.loadClass(Unknown Source)
at mod_IC2.initialize(mod_IC2.java:306)
at ic2.platform.Ic2.load(Ic2.java:65)
at ModLoader.init(ModLoader.java:824)
at ModLoader.AddAllRenderers(ModLoader.java:189)
at afq.<init>(afq.java:80)
at afq.<clinit>(afq.java:9)
at net.minecraft.client.Minecraft.a(Minecraft.java:316)
at net.minecraft.client.Minecraft.run(Minecraft.java:620)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: forge.IUseItemFirst
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 java.lang.ClassLoader.loadClass(Unknown Source)
... 20 more