Whenever I try to play Minecraft with this mod installed it crashes. Not sure if I'm doing something wrong or what.

Please post the crash logs and information about Minecraft version and all installed mods with crash reports.

I am running Minecraft Forge Version 1.7.2, and using TooManyItems (Forge) version 1.7.2, Treecapitator (Universal) Version 1.7.2.r01, and bspkrsCor (Universal) Version 6.0 (1.7.2).

---- Minecraft Crash Report ----
// Oops.

Time: 3/1/14 8:37 PM
Description: There was a severe problem during mod loading that has caused the game to fail

cpw.mods.fml.common.LoaderException: java.lang.ClassNotFoundException: invtweaks.forge.ClientProxy
at cpw.mods.fml.common.ProxyInjector.inject(ProxyInjector.java:76)
at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:515)
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 com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
at com.google.common.eventbus.EventBus.post(EventBus.java:267)
at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:209)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:188)
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 com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
at com.google.common.eventbus.EventBus.post(EventBus.java:267)
at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:119)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:484)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:201)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:498)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:853)
at net.minecraft.client.main.Main.main(SourceFile:103)
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: invtweaks.forge.ClientProxy
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:188)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at cpw.mods.fml.common.ModClassLoader.loadClass(ModClassLoader.java:58)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at cpw.mods.fml.common.ProxyInjector.inject(ProxyInjector.java:59)
... 33 more
Caused by: java.lang.NoClassDefFoundError: cpw/mods/fml/common/IPickupNotifier
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)
... 39 more
Caused by: java.lang.ClassNotFoundException: cpw.mods.fml.common.IPickupNotifier
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:188)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 43 more
Caused by: java.lang.NullPointerException
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:180)
... 45 more

A detailed walkthrough of the error, its code path and all known details is as follows:

-- System Details --
Details:
Minecraft Version: 1.7.2
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 33853296 bytes (32 MB) / 153739264 bytes (146 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.01-pre FML v7.2.125.1034 Minecraft Forge 10.12.0.1034 7 mods loaded, 7 mods active
mcp{8.09} Minecraft Coder Pack Unloaded->Constructed
FML{7.2.125.1034} Forge Mod Loader Unloaded->Constructed
Forge{10.12.0.1034} Minecraft Forge Unloaded->Constructed
bspkrsCore{6.0(1.7.2)} bspkrsCore Unloaded->Constructed
TreeCapitator{1.7.2.r01} TreeCapitator Unloaded->Constructed
inventorytweaks{1.56} Inventory Tweaks Unloaded->Errored
TooManyItems{1.7.2} TooManyItems Unloaded->Constructed

That is a 1.6 version of InvTweaks, not a 1.7 version.

OK thanks for the help.