crash report mystcraft

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 25/12/12 3.35
Description: Exception in server tick loop

java.lang.IllegalAccessError: tried to access field yc.n from class xcompwiz.mystcraft.WorldProviderMyst
	at xcompwiz.mystcraft.WorldProviderMyst.updateWeather(WorldProviderMyst.java:327)
	at xcompwiz.mystcraft.WorldProviderMyst.calculateInitialWeather(WorldProviderMyst.java:314)
	at yc.a(World.java:2963)
	at yc.<init>(World.java:334)
	at in.<init>(WorldServer.java:103)
	at ih.<init>(SourceFile:10)
	at net.minecraftforge.common.DimensionManager.initDimension(DimensionManager.java:168)
	at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:757)
	at xcompwiz.mystcraft.MystLinkController.travelEntity(MystLinkController.java:33)
	at xcompwiz.mystcraft.ItemLinking.activate(ItemLinking.java:65)
	at xcompwiz.mystcraft.ContainerBook.processMessage(ContainerBook.java:182)
	at xcompwiz.mystcraft.MPacketGUIMessage.handle(MPacketGUIMessage.java:34)
	at xcompwiz.mystcraft.MystcraftPacketHandler.onPacketData(MystcraftPacketHandler.java:43)
	at cpw.mods.fml.common.network.NetworkRegistry.handlePacket(NetworkRegistry.java:243)
	at cpw.mods.fml.common.network.NetworkRegistry.handleCustomPacket(NetworkRegistry.java:233)
	at cpw.mods.fml.common.network.FMLNetworkHandler.handlePacket250Packet(FMLNetworkHandler.java:71)
	at iv.a(NetServerHandler.java:1107)
	at di.a(SourceFile:59)
	at cf.b(MemoryConnection.java:80)
	at iv.d(NetServerHandler.java:136)
	at iw.b(NetworkListenThread.java:57)
	at bec.b(IntegratedServerListenThread.java:108)
	at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:702)
	at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:598)
	at bdz.q(IntegratedServer.java:123)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
	at fy.run(SourceFile:849)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 1.4.6
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_09, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 223559024 bytes (213 MB) / 537821184 bytes (512 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 12150 (680400 bytes; 0 MB) allocated, 3759 (210504 bytes; 0 MB) used
	Suspicious classes: FML and Forge are installed
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	FML: MCP v7.25 FML v4.6.12.511 Minecraft Forge 6.5.0.471 4 mods loaded, 4 mods active
	mcp [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available->Available->Available->Available->Available->Available
	FML [Forge Mod Loader] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available->Available->Available->Available->Available->Available
	Forge [Minecraft Forge] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available->Available->Available->Available->Available->Available
	Mystcraft [Mystcraft] (mystcraft-uni-1.4.6-0.9.5.00.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available->Available->Available->Available->Available->Available
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 2930 (164080 bytes; 0 MB) allocated, 2505 (140280 bytes; 0 MB) used
	Player Count: 1 / 8; [iq[''/6533, l='New World', x=68,50, y=64,00, z=247,50]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Definitely; Client brand changed to 'forge,fml'