<p> This Serializable class is an inner class of a non-serializable class.
Thus, attempts to serialize it will also attempt to associate instance of the outer
class with which it is associated, leading to a runtime error.
</p>
<p>If possible, making the inner class a static inner class should solve the 
problem. Making the outer class serializable might also work, but that would
mean serializing an instance of the inner class would always also serialize the instance
of the outer class, which it often not what you really want.