Cluster manager error

Dear All,

I run 2 openfire server, and 1 database server using mysql. I have configured the clustering plugin and seems everthings is OK. Right now my server handle about 18,000 concurrent user, but sometimes i found this error message on my log and when it’s happend my cluster is getting Not Availabe. Can anybody help me, why it’s happend? What should I do? Because i’m getting frustation about it…

2010.10.06 11:41:37 [org.jivesoftware.openfire.event.SessionEventDispatcher.dispatchEvent(SessionEv entDispatcher.java:87)]
java.lang.IllegalStateException: Requested node not found in cluster
at com.jivesoftware.util.cache.CoherenceClusteredCacheFactory.doSynchronousCluster Task(CoherenceClusteredCacheFactory.java:304)
at org.jivesoftware.util.cache.CacheFactory.doSynchronousClusterTask(CacheFactory. java:523)
at com.jivesoftware.openfire.session.RemoteSession.doSynchronousClusterTask(Remote Session.java:171)
at com.jivesoftware.openfire.session.RemoteSession.getStreamID(RemoteSession.java: 77)
at org.jivesoftware.openfire.multiplex.ConnectionMultiplexerManager.removeSession( ConnectionMultiplexerManager.java:308)
at org.jivesoftware.openfire.multiplex.ConnectionMultiplexerManager.sessionDestroy ed(ConnectionMultiplexerManager.java:299)
at org.jivesoftware.openfire.event.SessionEventDispatcher.dispatchEvent(SessionEve ntDispatcher.java:67)
at org.jivesoftware.openfire.SessionManager.removeSession(SessionManager.java:1056 )
at com.jivesoftware.util.cache.ClusterListener.cleanupNode(ClusterListener.java:34 9)
at com.jivesoftware.util.cache.ClusterListener.memberLeft(ClusterListener.java:291 )
at com.tangosol.net.MemberEvent.dispatch(MemberEvent.java:151)
at com.tangosol.coherence.component.util.SafeService.translateEvent(SafeService.CD B:13)
at com.tangosol.coherence.component.util.SafeService.memberLeft(SafeService.CDB:1)
at com.tangosol.net.MemberEvent.dispatch(MemberEvent.java:151)
at com.tangosol.coherence.component.util.daemon.queueProcessor.Service$DispatchMem berEvent.run(Service.CDB:1)
at com.tangosol.coherence.component.util.daemon.queueProcessor.Service$EventDispat cher.onNotify(Service.CDB:17)
at com.tangosol.coherence.component.util.Daemon.run(Daemon.CDB:35)
at java.lang.Thread.run(Thread.java:619)