As I'm guessing you know. passivation errors are generally caused by member variables that are not serializable. I'm not familiar with the jaxen library but is there a possibility that you have a non-serializable member variable that uses the library?
org.apache.log4j.Logger is NOT seriazable.
You can add code to your life-cycle methods to set the variables to null on passivation and create them on activation. Or you can declare the member variable to be transient so that the container will not try to write it out on passivation.
Hope this helps.