Tomcat6.0.18集群下的oscache的配置问题
环境配置：
1、配置了两份tomcat6.0.18，按照文档做了集群配置；
2、实现了与apache2.2.8的整合，启用了session复制。
3、在应用中增加oscache时，出现了如下的问题提示：
严重: Unable to apply diff to key:033AA16CBA6E71EFAD4B745938970F2B.tomcat_1
java.lang.NullPointerException
at com.opensymphony.oscache.base.algorithm.LRUCache.itemPut(LRUCache.java:90)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.put(AbstractConcurrentReadCache.java:1619)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.put(AbstractConcurrentReadCache.java:864)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.readObject(AbstractConcurrentReadCache.java:1210)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1849)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1947)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1871)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
at org.apache.catalina.ha.session.DeltaRequest$AttributeInfo.readExternal(DeltaRequest.java:361)
at org.apache.catalina.ha.session.DeltaRequest.readExternal(DeltaRequest.java:255)
at org.apache.catalina.ha.session.DeltaSession.applyDiff(DeltaSession.java:171)
at org.apache.catalina.tribes.tipis.AbstractReplicatedMap.messageReceived(AbstractReplicatedMap.java:626)
at org.apache.catalina.tribes.group.GroupChannel.messageReceived(GroupChannel.java:269)
at org.apache.catalina.tribes.group.ChannelInterceptorBase.messageReceived(ChannelInterceptorBase.java:79)
at org.apache.catalina.tribes.group.interceptors.TcpFailureDetector.messageReceived(TcpFailureDetector.java:110)
at org.apache.catalina.tribes.group.ChannelInterceptorBase.messageReceived(ChannelInterceptorBase.java:79)
at org.apache.catalina.tribes.group.ChannelInterceptorBase.messageReceived(ChannelInterceptorBase.java:79)
at org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor.messageReceived(ThroughputInterceptor.java:86)
at org.apache.catalina.tribes.group.ChannelInterceptorBase.messageReceived(ChannelInterceptorBase.java:79)
at org.apache.catalina.tribes.group.ChannelCoordinator.messageReceived(ChannelCoordinator.java:241)
at org.apache.catalina.tribes.transport.ReceiverBase.messageDataReceived(ReceiverBase.java:225)
at org.apache.catalina.tribes.transport.nio.NioReplicationTask.drainChannel(NioReplicationTask.java:18
at org.apache.catalina.tribes.transport.nio.NioReplicationTask.run(NioReplicationTask.java:91)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:90
at java.lang.Thread.run(Thread.java:619)
以为是oscache没有配置集群的问题，修改配置后，问题依旧，一直报如上的错误，google、baidu都试了，文档也看了，找不出问题来，哪位遇到过类似的情况，请不吝赐教，目前心急如焚啊
