i just encountered a serious bug.. Galacticraft is using the same Dimension ID (-28) as some other mod that i cant identify. I think its Dimensional Doors. but im really not sure. In any case, it ruins your entire world if it happens :/
java.lang.IllegalArgumentException: Failed to register dimension for id -28, One is already registered
at net.minecraftforge.common.DimensionManager.registerDimension(DimensionManager.java:127)
at micdoodle8.mods.galacticraft.core.network.GCCorePacketHandlerClient.onPacketData(GCCorePacketHandlerClient.java:398)
at cpw.mods.fml.common.network.NetworkRegistry.handlePacket(NetworkRegistry.java:255)
at cpw.mods.fml.common.network.NetworkRegistry.handleCustomPacket(NetworkRegistry.java:245)
at cpw.mods.fml.common.network.FMLNetworkHandler.handlePacket250Packet(FMLNetworkHandler.java:85)
at net.minecraft.client.multiplayer.NetClientHandler.func_72501_a(NetClientHandler.java:1651)
at net.minecraft.network.packet.Packet250CustomPayload.func_73279_a(SourceFile:61)
at net.minecraft.network.TcpConnection.func_74428_b(TcpConnection.java:462)
at net.minecraft.client.multiplayer.NetClientHandler.func_72551_d(NetClientHandler.java:281)
at net.minecraft.client.multiplayer.GuiConnecting.func_73876_c(GuiConnecting.java:51)
at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1580)
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:910)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:838)
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)