系统运行出现java.lang.NoClassDefFoundError: Lorg/jvnet/staxex/XMLStreamReaderEx异常

求大神帮忙 ，我的系统启动之后 运行几天就会出现如下异常，重启之后就没有了，几天之后又会出现，求帮忙分析下是什么原因?
2013-09-24 14:54:59 ERROR org.apache.coyote.http11.Http11Processor - Error processing request
java.lang.NoClassDefFoundError: Lorg/jvnet/staxex/XMLStreamReaderEx;
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
at java.lang.Class.getDeclaredFields(Class.java:1743)
at com.esotericsoftware.kryo.serialize.FieldSerializer.rebuildCachedFields(FieldSerializer.java:61)
at com.esotericsoftware.kryo.serialize.FieldSerializer.<init>(FieldSerializer.java:48)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.<init>(ReferenceFieldSerializer.java:26)
at de.javakaffee.kryoserializers.KryoReflectionFactorySupport.newDefaultSerializer(KryoReflectionFactorySupport.java:48)
at com.esotericsoftware.kryo.Kryo.newSerializer(Kryo.java:273)
at de.javakaffee.web.msm.serializer.kryo.KryoTranscoder$1.newSerializer(KryoTranscoder.java:155)
at com.esotericsoftware.kryo.Kryo.handleUnregisteredClass(Kryo.java:329)
at de.javakaffee.web.msm.serializer.kryo.KryoTranscoder$1.handleUnregisteredClass(KryoTranscoder.java:172)
at com.esotericsoftware.kryo.Kryo.getRegisteredClass(Kryo.java:305)
at com.esotericsoftware.kryo.Kryo.writeClass(Kryo.java:374)
at de.javakaffee.kryoserializers.ClassSerializer.write(ClassSerializer.java:51)
at de.javakaffee.kryoserializers.ClassSerializer.write(ClassSerializer.java:30)
at com.esotericsoftware.kryo.serialize.SimpleSerializer.writeObjectData(SimpleSerializer.java:17)
at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:489)
at com.esotericsoftware.kryo.serialize.CollectionSerializer.writeObjectData(CollectionSerializer.java:86)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:175)
at com.esotericsoftware.kryo.serialize.ReferenceFieldSerializer.writeObjectData(ReferenceFieldSerializer.java:52)
at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:489)
at com.esotericsoftware.kryo.serialize.MapSerializer.writeObjectData(MapSerializer.java:104)
at com.esotericsoftware.kryo.Serializer.writeObject(Serializer.java:43)
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:520)
at com.esotericsoftware.kryo.ObjectBuffer.writeObject(ObjectBuffer.java:251)
at de.javakaffee.web.msm.serializer.kryo.KryoTranscoder.serializeAttributes(KryoTranscoder.java:272)
at de.javakaffee.web.msm.TranscoderService.serializeAttributes(TranscoderService.java:153)
at de.javakaffee.web.msm.BackupSessionTask.serializeAttributes(BackupSessionTask.java:175)
at de.javakaffee.web.msm.BackupSessionTask.call(BackupSessionTask.java:109)
at de.javakaffee.web.msm.BackupSessionTask.call(BackupSessionTask.java:50)
at de.javakaffee.web.msm.BackupSessionService$SynchronousExecutorService.submit(BackupSessionService.java:346)
at de.javakaffee.web.msm.BackupSessionService.backupSession(BackupSessionService.java:205)
at de.javakaffee.web.msm.MemcachedSessionService.backupSession(MemcachedSessionService.java:1076)
at de.javakaffee.web.msm.RequestTrackingHostValve.backupSession(RequestTrackingHostValve.java:244)
at de.javakaffee.web.msm.RequestTrackingHostValve.invoke(RequestTrackingHostValve.java:173)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: org.jvnet.staxex.XMLStreamReaderEx
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
... 52 moreXMLStreamReaderEx