I'm downloaded jboss-3.0.0RC1_tomcat-4.0.3 as well - and I get the same behaviour. I set a session attribute in servlet - then forward/redirect to a jsp - and the value of the attribute is null when accessed in the jsp! I get different values for session.getId() when invoked from servlet and then later from the jsp. My session-timeout is set to 60min - default for tomcat is 30min I believe.
Furthrermore, we never got this error when using previous beta-release with tomcat-4.0.2.
Is this a bug?