That can happen if you use server state saving and the view has disappeared from session for some reason (e.g. session expiration). If you refresh the whole page the error should disappear. Please consider reading that: http://www.jboss.org/file-access/default/members/jbossrichfaces/freezone/docs/devguide/en/html/ArchitectureOverview.html#RequestErrorsAndSessionExpirationHandling
Thanks a lot.
I solved the problem when I change tomcat to JBOSS...
But I don't know why.