Why am I getting error while trying to access a portal on Liferay 4.2.1?

I'm trying to cluster Web Session on Liferay 4.2.1. I've followed the specifications in the documentation.

When I try to access the portal I get a :

ERROR [org.apache.catalina.core.ContainerBase.[Catalina].[local.host].[/].[MainServlet]] Servlet.service() for servlet MainServlet threw exception

java.lang.RuntimeException: java.io.NotSerializableException: com.liferay.portal.kernel.servlet.PortletSessionTracker
        at com.terracotta.session.SerializedAttributeStore$SerializedAttribute.<init>(SerializedAttributeStore.java:98)
        at com.terracotta.session.SerializedAttributeStore$SerializedAttributeWithCache.<init>(SerializedAttributeStore.java:141)
        at com.terracotta.session.SerializedAttributeStore.put(SerializedAttributeStore.java:60)
        at com.terracotta.session.SessionData.bindAttribute(SessionData.java:455)
        at com.terracotta.session.SessionData.setAttributeReturnOld(SessionData.java:322)
        at com.terracotta.session.SessionData.setAttribute(SessionData.java:313)
        at com.liferay.portal.servlet.MainServlet.service(MainServlet.java:581)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at com.portal.filter.LoginProcessFilter.doFilter(LoginProcessFilter.java:123)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at com.liferay.filters.secure.SecureFilter.doFilter(SecureFilter.java:143)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at com.portal.filter.ClientHibernateFilter.doFilter(ClientHibernateFilter.java:74)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
        at org.terracotta.modules.tomcat.tomcat_5_5.SessionValve55.tcInvoke(SessionValve55.java:99)
        at o开发者_如何学编程rg.terracotta.modules.tomcat.tomcat_5_5.SessionValve55.invoke(SessionValve55.java:85)
        at org.terracotta.session.ModernTomcatSessionValve.invoke(ModernTomcatSessionValve.java:66)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
        at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
        at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
        at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
        at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
        at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.NotSerializableException: com.liferay.portal.kernel.servlet.PortletSessionTracker
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
        at org.terracotta.cache.serialization.DsoSerializationStrategy.serialize(DsoSerializationStrategy.java:61)
        at com.terracotta.session.SerializedAttributeStore$SerializedAttribute.<init>(SerializedAttributeStore.java:96)
        ... 35 more

Any help is appreciated.

Thank you.

Update: Apparently Liferay 4.2.1 is not supported by Terracotta as it is too old. Suggestions would be to switch to the latest Liferay version(6).