i recently installed ProjectRed Mechanical. But whenever i open my game now it just crashes. Here is the crash report i get when the game crashes:
---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 2/22/14 11:57 PM
Description: Initializing game

java.lang.NoClassDefFoundError: mrtjp/projectred/api/ITransportationAPI
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at cpw.mods.fml.common.ProxyInjector.inject(ProxyInjector.java:42)
at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:524)
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:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
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:201)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:181)
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:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
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:112)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:511)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:183)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:473)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:808)
at net.minecraft.client.main.Main.main(SourceFile:101)
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:131)
at net.minecraft.launchwrapper.Launch.main(Launch.java:27)
Caused by: java.lang.ClassNotFoundException: mrtjp.projectred.api.ITransportationAPI
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:186)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 36 more
Caused by: java.lang.NullPointerException
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:178)
... 38 more

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

-- Head --
Stacktrace:
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at cpw.mods.fml.common.ProxyInjector.inject(ProxyInjector.java:42)
at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:524)
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:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
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:201)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:181)
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:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
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:112)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:511)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:183)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:473)

-- Initialization --
Details:
Stacktrace:
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:808)
at net.minecraft.client.main.Main.main(SourceFile:101)
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:131)
at net.minecraft.launchwrapper.Launch.main(Launch.java:27)

-- System Details --
Details:
Minecraft Version: 1.6.4
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_45, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 198694488 bytes (189 MB) / 368574464 bytes (351 MB) up to 954728448 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: FML and Forge are installed
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v8.11 FML v6.4.49.965 Minecraft Forge 9.11.1.965 28 mods loaded, 28 mods active
mcp{8.09} Minecraft Coder Pack Unloaded->Constructed
FML{6.4.49.965} Forge Mod Loader Unloaded->Constructed
Forge{9.11.1.965} Minecraft Forge Unloaded->Constructed
CodeChickenCore{0.9.0.6} CodeChicken Core Unloaded->Constructed
NotEnoughItems{1.6.1.5} Not Enough Items Unloaded->Constructed
OpenModsCore{0.2} OpenModsCore Unloaded->Constructed
TConstruct-Preloader{0.0.1} Tinkers Corestruct Unloaded->Constructed
mod_ReiMinimap{v3.4_01 [1.6.2]} mod_ReiMinimap Unloaded->Constructed
CoFHCore{2.0.0.2} CoFH Core Unloaded->Constructed
CoFHLoot{2.0.0.2} CoFH Loot Unloaded->Constructed
CoFHMasquerade{2.0.0.2} CoFH Masquerade Unloaded->Constructed
CoFHSocial{2.0.0.2} CoFH Social Unloaded->Constructed
CoFHWorld{2.0.0.2} CoFH World Unloaded->Constructed
Hats{2.1.3} Hats Unloaded->Constructed
Morph{0.7.0} Morph Unloaded->Constructed
OpenMods{0.2} OpenMods Unloaded->Constructed
OpenBlocks{1.2.5} OpenBlocks Unloaded->Constructed
ProjRed|Expansion{1.0} ProjRed|Expansion Unloaded
ProjRed|Transportation{1.0} ProjRed|Transportation Unloaded
ForgeMultipart{1.0.0.219} Forge Multipart Unloaded
ThermalExpansion{3.0.0.2} Thermal Expansion Unloaded
Waila{1.5.1} Waila Unloaded
TConstruct{1.6.X_1.5.2.1} Tinkers' Construct Unloaded
witchery{0.14.0} Witchery Unloaded
McMultipart{1.0.0.219} Minecraft Multipart Plugin Unloaded
CustomOreGenRevived{1.0.21} Custom Ore Generation: First Revival Unloaded
mod_CustomOreGen{Not available} mod_CustomOreGen Unloaded
ForgeMicroblock{1.0.0.219} Forge Microblocks Unloaded
Launched Version: 1.6.4-Forge9.11.1.965
LWJGL: 2.9.0
OpenGL: AMD Radeon(TM) HD 6520G GL version 4.1.11156 Compatibility Profile Context, ATI Technologies Inc.
Is Modded: Definitely; Client brand changed to 'fml,forge'
Type: Client (map_client.txt)
Resource Pack: Default
Current Language: English (UK)
Profiler Position: N/A (disabled)
Vec3 Pool Size: ERROR NullPointerException: null

All your jars have to be he same version.