Entry Distribution Requirements
Entry data distributed among members of the distributed system must be serializable. Entry keys and values are serialized for distribution.
If a client defines a region, it must register any serializable types for all classes of objects stored in the region. This includes entries that the application gets or puts, as well as entries that are pushed to the client’s cache automatically through distribution. The types must be registered before the client connects to the distributed system.
See Serializing Data for more information about these requirements.