I was trying to fix my mods and stuff because I messed up trying to get my mods from 1.6.2 to 1.6.4, when suddenly it messed up and gave this error, more information is in the log.
Caused by: java.lang.NoClassDefFoundError: cpw/mods/fml/common/registry/GameData
[13:16:18 INFO]: Client> at net.minecraft.item.Item.<init>(Item.java:274)
[13:16:18 INFO]: Client> at net.minecraft.item.ItemTool.<init>(ItemTool.java:28)
[13:16:18 INFO]: Client> at net.minecraft.item.ItemSpade.<init>(SourceFile:11)
[13:16:18 INFO]: Client> at net.minecraft.item.Item.<clinit>(Item.java:48)
[13:16:18 INFO]: Client> at net.minecraft.block.Block.<clinit>(Block.java:1426)
[13:16:18 INFO]: Client> at net.minecraft.stats.StatList.func_75921_a(StatList.java:185)
[13:16:18 INFO]: Client> at net.minecraft.stats.StatList.<clinit>(StatList.java:96)
[13:16:18 INFO]: Client> at net.minecraft.client.Minecraft.<init>(Minecraft.java:328)
[13:16:18 INFO]: Client> at net.minecraft.client.main.Main.main(SourceFile:83)
Edit: Mediafire link, since I couldn't attach the log file:
http://www.mediafire.com/view/d5nuh2ko7z72szm/ForgeModLoader-client-0.log
Edit2: Fixed...