Q: What is this iPlanet error?
   SERVLET-put_nonserial: Putting non-serializable object ... when using NAS session?

A: This is a known issue with iPlanet iAS (6.x). By default, iPlanet distributes
   the session context across the server instances (even if you have only one
   instance) and thus all objects in the session have to be serializable.
   Solution: Disable the distribution of the session context, i.e., uncheck the 
             Distributed Session check box on the IAS tab of the editing 
             discriptor panel.
             You then need save the descriptor and redeploy the application. 

   Note that, you do not have to do that anymore for later Bugzero versions,
   distributed session is now supported.