I didn't know if I needed to post this here or with Tinker's construct but seeing as i added this mod most recently I decided to post it here. Adding this mod to my game causes me to get NoClassDefFoundError for tinkers construct items.

Time: 7/24/14 3:39 PM
Description: Initializing game

java.lang.NoClassDefFoundError: tconstruct/tools/items/Manual
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at cpw.mods.fml.common.registry.ObjectHolderRegistry.scanTarget(ObjectHolderRegistry.java:70)
at cpw.mods.fml.common.registry.ObjectHolderRegistry.findObjectHolders(ObjectHolderRegistry.java:39)
at cpw.mods.fml.common.Loader.preinitializeMods(Loader.java:507)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:239)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:480)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:867)
at net.minecraft.client.main.Main.main(SourceFile:148)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:134)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
Caused by: java.lang.ClassNotFoundException: tconstruct.tools.items.Manual
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:188)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 15 more
Caused by: java.lang.NoClassDefFoundError: mantle/items/abstracts/CraftingItem
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:180)
... 17 more
Caused by: java.lang.ClassNotFoundException: mantle.items.abstracts.CraftingItem
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:99)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 21 more

It's a TC crash.

You have a outdated version of Forge, just update to the newest, then it should work :3

This is indeed a Forge requirement crash. I thought it used to stop the game loading when a requirement wasn't met, but now it seems to just prevent loading a world. Just follow the required (or above) Forge build listed with the downloads and it will load up just fine.