I've created multiple mods under the same workspace which use eachother. However, when updating to the latest version of Forge, whenever I run it it will throw this error:

cpw.mods.fml.common.LoaderException: java.lang.IllegalArgumentException: Can not set static info.mineverse.willow.sabers.SaberBase field info.mineverse.willow.sabers.SaberBase.instance to info.mineverse.willow.hats.Hats
at cpw.mods.fml.common.LoadController.transition(LoadController.java:102)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:459)
at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:144)
at net.minecraft.client.Minecraft.startGame(Minecraft.java:405)
at net.minecraft.client.Minecraft.run(Minecraft.java:737)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.IllegalArgumentException: Can not set static info.mineverse.willow.sabers.SaberBase field info.mineverse.willow.sabers.SaberBase.instance to info.mineverse.willow.hats.Hats
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
at sun.reflect.UnsafeStaticObjectFieldAccessorImpl.set(Unknown Source)
at java.lang.reflect.Field.set(Unknown Source)
at cpw.mods.fml.common.FMLModContainer.parseSimpleFieldAnnotation(FMLModContainer.java:329)
at cpw.mods.fml.common.FMLModContainer.processFieldAnnotations(FMLModContainer.java:255)
at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:349)
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 com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:69)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:317)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:300)
at com.google.common.eventbus.EventBus.post(EventBus.java:268)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:124)
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 com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:69)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:317)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:300)
at com.google.common.eventbus.EventBus.post(EventBus.java:268)
at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:81)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:458)
... 4 more
--- END ERROR REPORT a1bfc336 ----------

 

The Mods in the error change at what seems like random to any of the mods, even ones which aren't linked what so ever. What could the cause of this be?

Your @Instance needs a modid parameter