Forge crashes when using mod

I've been trying to get my mod to work with forge, and it works when you use it in MCP, but as soon as I try in client mode, MC crashes. Is there something that the SRC files don't need but mod files do need?

---- Minecraft Crash Report ----
// I feel sad now 

Time: 8/16/12 7:30 PM
Description: Failed to start game

cpw.mods.fml.common.LoaderException
at cpw.mods.fml.common.Loader.identifyDuplicates(Loader.java:332)
at cpw.mods.fml.common.Loader.identifyMods(Loader.java:295)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:414)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:192)
at net.minecraft.client.Minecraft.a(Minecraft.java:402)
at net.minecraft.client.Minecraft.run(Minecraft.java:734)
at java.lang.Thread.run(Unknown Source)

Relevant Details:
- Minecraft Version: 1.3.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.6.0_25, Sun Microsystems Inc.
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
- Memory: 418063224 bytes (398 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xmx1024m -Xms512m
- LWJGL: 2.4.2
- OpenGL: GeForce 6150SE nForce 430/PCI/SSE2 GL version 2.1.2, NVIDIA Corporation
- Is Modded: Definitely; 'forge,fml'
- Type: Client
- Texture Pack: Default
- Profiler Position: N/A (disabled)