Bug: [1.15] Crash on startup (Different than the others)

1st Official Post

    Bug: I installed IC2 with the JAR file, it's in my mods folder. When I start up, I get this error though:

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    java.lang.NoClassDefFoundError: forge/ISidedInventory
    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.(mod_IC2.java:34)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at ModLoader.addMod(ModLoader.java:275)
    at ModLoader.readFromModFolder(ModLoader.java:1179)
    at ModLoader.init(ModLoader.java:824)
    at ModLoader.AddAllRenderers(ModLoader.java:186)
    at aam.(aam.java:61)
    at aam.(aam.java:10)
    at net.minecraft.client.Minecraft.a(SourceFile:259)
    at net.minecraft.client.Minecraft.run(SourceFile:629)
    at java.lang.Thread.run(Unknown Source)
    Caused by: java.lang.ClassNotFoundException: forge.ISidedInventory
    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) ... 27 more


    I have these mods installed:
    *BuildCraft
    *TooManyItems
    *SinglePlayerCommands
    All of these are updated, is it possible it may be conflicting with it?
    Please and thanks ;D</init>