what causes this exception ???

com.intellij.openapi.util.InvalidDataException: com.intellij.openapi.util.InvalidDataException
com.intellij.openapi.components.impl.stores.InvalidComponentDataException: com.intellij.openapi.util.InvalidDataException
 at com.intellij.openapi.components.impl.stores.ComponentStoreImpl.initJdomExternalizable(ComponentStoreImpl.java:200)
 at com.intellij.openapi.components.impl.stores.ComponentStoreImpl$1.run(ComponentStoreImpl.java:92)
 at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:691)
 at com.intellij.openapi.components.impl.stores.ComponentStoreImpl.initComponent(ComponentStoreImpl.java:102)
 at com.intellij.openapi.components.impl.ComponentManagerImpl.a(ComponentManagerImpl.java:238)
 at com.intellij.openapi.components.impl.ComponentManagerImpl.access$1200(ComponentManagerImpl.java:60)
 at com.intellij.openapi.components.impl.ComponentManagerImpl$ComponentConfigComponentAdapter$1.getComponentInstance(ComponentManagerImpl.java:640)
 at com.intellij.openapi.components.impl.ComponentManagerImpl$ComponentConfigComponentAdapter.getComponentInstance(ComponentManagerImpl.java:585)
 at com.intellij.util.pico.DefaultPicoContainer.getLocalInstance(DefaultPicoContainer.java:231)
 at com.intellij.util.pico.DefaultPicoContainer.getInstance(DefaultPicoContainer.java:218)
 at com.intellij.util.pico.DefaultPicoContainer.getComponentInstance(DefaultPicoContainer.java:200)
 at org.picocontainer.alternatives.AbstractDelegatingMutablePicoContainer.getComponentInstance(AbstractDelegatingMutablePicoContainer.java:75)