ZK - Open Source Ajax Java Framework

Hello,
when i sto the tomcat i receive a lot of this error:

SEVERE: Unable to serialize entry: z_bshnsw=org.zkoss.zk.scripting.bsh.NSWrapSR@126f3d83

Why?

I have the same problem:
org.zkoss.io.Serializables smartWrite:64
SEVERE: Unable to serialize entry: z__ul_0=[GIORNALE MAGAZZINO LUGLIO 2010 .pdf.p7m]
2011-12-27 17:33:02,823 ERROR [org.jboss.web.tomcat.service.session.JBossCacheService] externalizeSession(): exception occurred externalizing session SessionBasedClusteredSession[id: 3DD28FE0BECD6395848AE150641746D7.ext2 lastAccessedTime: 132500381284 version: 368 lastOutdated: 0]
java.io.NotSerializableException: org.zkoss.zk.au.http.ZkFileItemFactory

I'm working in a jboss instance on a cluster enviroment and in the zk.xml i've already configured the SerializableUiFactory like described here:
http://books.zkoss.org/wiki/ZK_Developer%27s_Reference/Clustering/ZK_Configuration

Thanks for helping me

it seems that org.zkoss.zk.scripting.bsh class doesn't implements Serialization and so we get this errors.
Someone has tried also to recompile zk adding the implements on that class but even if you get no more errors you will have a lot of side effects..