Serializing problem in Hazelcast

I’m using hazelcast plugin, and the clustering is working but I encountered an error.

I debug it, the error happens in file RosterManager.java, function getRoster(String username), at line Roster roster = rosterCache.get(username);

It throws an exception: com.hazelcast.nio.hazelcastserializationexception problem when serializing type 1

Anyone can help me? what should I do next?

I found this exception when get roster or update roster =>

2013.07.19 14:20:55 org.jivesoftware.openfire.handler.PresenceSubscribeHandler - Internal server error

com.hazelcast.nio.HazelcastSerializationException: java.lang.NullPointerException

at com.hazelcast.nio.AbstractSerializer.toByte(AbstractSerializer.java:111)

at com.hazelcast.nio.AbstractSerializer.toByteArray(AbstractSerializer.java:139)

at com.hazelcast.nio.Serializer.writeObject(Serializer.java:56)

at com.hazelcast.impl.ThreadContext.toData(ThreadContext.java:131)

at com.hazelcast.nio.IOUtil.toData(IOUtil.java:139)

at com.hazelcast.impl.BaseManager$RequestBasedCall.setLocal(BaseManager.java:512)

at com.hazelcast.impl.BaseManager$ResponseQueueCall.setLocal(BaseManager.java:544)

at com.hazelcast.impl.ConcurrentMapManager$MPut.txnalPut(ConcurrentMapManager.java :1874)

at com.hazelcast.impl.ConcurrentMapManager$MPut.txnalPut(ConcurrentMapManager.java :1828)

at com.hazelcast.impl.ConcurrentMapManager$MPut.put(ConcurrentMapManager.java:1690 )

at com.hazelcast.impl.MProxyImpl$MProxyReal.put(MProxyImpl.java:634)

at com.hazelcast.impl.MProxyImpl$MProxyReal.put(MProxyImpl.java:608)

at com.hazelcast.impl.MProxyImpl.put(MProxyImpl.java:173)

at com.hazelcast.impl.MProxyImpl.put(MProxyImpl.java:124)

at com.jivesoftware.util.cache.ClusteredCache.put(ClusteredCache.java:81)

at org.jivesoftware.util.cache.CacheWrapper.put(CacheWrapper.java:129)

at org.jivesoftware.openfire.roster.RosterManager$2.contactUpdated(RosterManager.j ava:449)

at org.jivesoftware.openfire.roster.RosterEventDispatcher.contactUpdated(RosterEve ntDispatcher.java:124)

at org.jivesoftware.openfire.roster.Roster.updateRosterItem(Roster.java:588)

&&&&&&&&

2013.07.19 14:39:58 org.jivesoftware.openfire.handler.PresenceUpdateHandler - Internal server error. Triggered by packet:

com.hazelcast.nio.HazelcastSerializationException: Problem when serializing type 1

at com.hazelcast.nio.AbstractSerializer.toObject(AbstractSerializer.java:128)

at com.hazelcast.nio.AbstractSerializer.toObject(AbstractSerializer.java:156)

at com.hazelcast.nio.Serializer.readObject(Serializer.java:75)

at com.hazelcast.impl.ThreadContext.toObject(ThreadContext.java:135)

at com.hazelcast.nio.IOUtil.toObject(IOUtil.java:163)

at com.hazelcast.impl.DefaultRecord.getValue(DefaultRecord.java:64)

at com.hazelcast.impl.ConcurrentMapManager$MGet.get(ConcurrentMapManager.java:1109 )

at com.hazelcast.impl.MProxyImpl$MProxyReal.get(MProxyImpl.java:783)

at com.hazelcast.impl.MProxyImpl.get(MProxyImpl.java:114)

at com.jivesoftware.util.cache.ClusteredCache.get(ClusteredCache.java:86)

at org.jivesoftware.util.cache.CacheWrapper.get(CacheWrapper.java:121)

at org.jivesoftware.openfire.roster.RosterManager.getRoster(RosterManager.java:154 )

at org.jivesoftware.openfire.handler.PresenceUpdateHandler.initSession(PresenceUpd ateHandler.java:362)

anyone help me, pleaseee???