Following exception in Tomcat6 log:

SEVERE: Exception loading sessions from persistent storage
java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: com.icesoft.faces.facelets.component.table.richdatagrid.FilterableSortableDataModel$PutMonitoringStringHashMap
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1332)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1870)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1870)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1870)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
at org.apache.catalina.session.StandardSession.readObject(StandardSession.java:1475)
at org.apache.catalina.session.StandardSession.readObjectData(StandardSession.java:977)
at org.apache.catalina.session.StandardManager.doLoad(StandardManager.java:394)
at org.apache.catalina.session.StandardManager.load(StandardManager.java:321)
at org.apache.catalina.session.StandardManager.start(StandardManager.java:643)
at org.apache.catalina.core.ContainerBase.setManager(ContainerBase.java:438)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4559)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:791)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:771)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:546)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:905)
at org.apache.catalina.startup.HostConfig.deployWARs(HostConfig.java:740)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:500)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1277)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:321)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1053)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:785)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:445)
at org.apache.catalina.core.StandardService.start(StandardService.java:519)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
at org.apache.catalina.startup.Catalina.start(Catalina.java:581)
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 org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
Caused by: java.io.NotSerializableException: com.icesoft.faces.facelets.component.table.richdatagrid.FilterableSortableDataModel$PutMonitoringStringHashMap
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
at org.apache.catalina.session.StandardSession.writeObject(StandardSession.java:1551)
at org.apache.catalina.session.StandardSession.writeObjectData(StandardSession.java:994)
at org.apache.catalina.session.StandardManager.doUnload(StandardManager.java:523)
at org.apache.catalina.session.StandardManager.unload(StandardManager.java:469)
at org.apache.catalina.session.StandardManager.stop(StandardManager.java:673)
at org.apache.catalina.core.StandardContext.stop(StandardContext.java:4774)
at org.apache.catalina.core.ContainerBase.removeChild(ContainerBase.java:924)
at org.apache.catalina.startup.HostConfig.undeployApps(HostConfig.java:1319)
at org.apache.catalina.startup.HostConfig.stop(HostConfig.java:1290)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:323)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1086)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1098)
at org.apache.catalina.core.StandardEngine.stop(StandardEngine.java:450)
at org.apache.catalina.core.StandardService.stop(StandardService.java:587)
at org.apache.catalina.core.StandardServer.stop(StandardServer.java:744)
at org.apache.catalina.startup.Catalina.stop(Catalina.java:648)
at org.apache.catalina.startup.Catalina.start(Catalina.java:615)
... 6 more