Granite DS erro no projeto de exemplo

Aew galera baxei o projeto de exemplo do site do granite ds fiz funcionar mas só esta inserindo registro no banco na hora de buscar da o seguinte erro

ArgumentError: Error #2173: Impossível ler o objeto em um fluxo. A classe org.granite.messaging.persistence.ExternalizablePersistentSet não implementa flash.utils.IExternalizable mas recebeu como alias uma classe externalizável.
at ObjectInput/readObject()
at test.granite.spring.entity::PersonBase/readExternal()[F:\JAVA\Netbeans\Flex\GUI\helloworldGraniteDSFlex\src\test\granite\spring\entity\PersonBase.as:87]
at ObjectInput/readObject()
at mx.collections::ArrayList/readExternal()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\collections\ArrayList.as:586]
at mx.collections::ArrayCollection/readExternal()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\collections\ArrayCollection.as:147]
at ObjectInput/readObject()
at mx.collections::ArrayList/readExternal()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\collections\ArrayList.as:586]
at mx.collections::ArrayCollection/readExternal()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\collections\ArrayCollection.as:147]

porque isso ocorre?