crash report

[SEVERE] Encountered an unexpected exception LoaderException
cpw.mods.fml.common.LoaderException: java.lang.NoSuchMethodError: argo.jdom.JsonNode.getFieldList()Ljava/util/List;
	at cpw.mods.fml.common.LoadController.transition(LoadController.java:147)
	at cpw.mods.fml.common.Loader.initializeMods(Loader.java:692)
	at cpw.mods.fml.server.FMLServerHandler.finishServerLoading(FMLServerHandler.java:93)
	at cpw.mods.fml.common.FMLCommonHandler.onServerStarted(FMLCommonHandler.java:355)
	at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:141)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:431)
	at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
Caused by: java.lang.NoSuchMethodError: argo.jdom.JsonNode.getFieldList()Ljava/util/List;
	at openperipheral.common.definition.DefinitionJsonMethod.<init>(DefinitionJsonMethod.java:79)
	at openperipheral.common.definition.DefinitionJsonClass.<init>(DefinitionJsonClass.java:29)
	at openperipheral.common.definition.DefinitionJsonMod.<init>(DefinitionJsonMod.java:25)
	at openperipheral.common.definition.DefinitionManager.load(DefinitionManager.java:26)
	at openperipheral.OpenPeripheral.init(OpenPeripheral.java:167)
	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 cpw.mods.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:494)
	at sun.reflect.GeneratedMethodAccessor2.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:74)
	at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
	at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
	at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
	at com.google.common.eventbus.EventBus.post(EventBus.java:267)
	at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:192)
	at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:172)
	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:74)
	at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
	at com.google.common.eventbus.EventBus.dispatch(EventBus.java:313)
	at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
	at com.google.common.eventbus.EventBus.post(EventBus.java:267)
	at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:103)
	at cpw.mods.fml.common.Loader.initializeMods(Loader.java:691)
	... 5 more