Having the same error. Server works fine, client crashes with similar config.
2012-09-04 20:24:00 [sEVERE] A critical error has occurred.
java.lang.NoClassDefFoundError: ProtectedProxy
at codechicken.chunkloader.mod_ChickenChunks.registerBlock(mod_ChickenChunks.java:111)
at codechicken.chunkloader.mod_ChickenChunks$1.tickStart(mod_ChickenChunks.java:69)
at cpw.mods.fml.common.SingleIntervalHandler.tickStart(SingleIntervalHandler.java:16)
at cpw.mods.fml.common.FMLCommonHandler.tickStart(FMLCommonHandler.java:164)
at cpw.mods.fml.client.FMLClientHandler.onRenderTickStart(FMLClientHandler.java:304)
at net.minecraft.client.Minecraft.x(Minecraft.java:874)
at net.minecraft.client.Minecraft.run(Minecraft.java:753)
at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.ClassNotFoundException: ProtectedProxy
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at org.spoutcraft.launcher.MinecraftClassLoader.findClass(MinecraftClassLoader.java:64)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 8 more