Are you sure that all references in the session are to Serializable objects? Perhaps this only occurs if the server tries to serialize the session and fails?
-no, I am not sure. At what time is the session serialized? I always thought that the session is alive and in memory for the specified time and then
released. I would say that we are only setting Strings and attach them to the session object. But I have to check first to find out.
The funny thing is that another installation for another customer is
working fine with the same application. The session timeout is different
thought. Might that be an explanation?
I really don't know how to interpret the bit with the different bahavior on another machine, are the loads similar?