[Opensymphony-oscache] Problems caching objects

Hi. I have an object, which is a bean with nested beans, but I can't 
cache it using OSCache. Here you have a code snippet.

Cache cache = sca.getCache(request, PageContext.APPLICATION_SCOPE);
String key = sca.generateEntryKey("mybean", request, 
PageContext.APPLICATION_SCOPE);
MyBean bean = null;
try {
        bean = (MyBean)cache.getFromCache(key);
} catch (NeedsRefreshException nre) {
        cache.cancelUpdate(key);
        bean = getBean();
        cache.putInCache(key, bean);
        //No exception thrown, it seems to be cached just fine
        try {
             //The object can be serialized and deserialized with no 
problems
            ObjectOutputStream oos = new ObjectOutputStream(new 
FileOutputStream("C:/temp/prueba.out"));
            oos.writeObject(categoryForm);
            ObjectInputStream ois = new ObjectInputStream(new 
FileInputStream("C:/temp/prueba.out"));
            MyBean bean2 = (MyBean)ois.readObject();
             //Try to get the cached object -> NeedRefreshException 
thrown, why???
             bean = (MyBean)cache.getFromCache(key);
        } catch (Exception e) {
            e.printStackTrace();
        }
}

If instead of a MyBean object I use another type of object, an 
ArrayList, for example, it works just fine. If I use memory caching 
only, it works, too. Other than implementing Serializable, is there any 
other requirements that an object needs to meet in order to be cached 
with HashDiskPersistenceListener?

I'm using OSCache 2.1.1. My oscache.properties looks like this:

cache.memory=false
cache.persistence.class=com.opensymphony.oscache.plugins.diskpersistence.HashDiskPersistenceListener
cache.path=c:\\temp\\cache
cache.algorithm=com.opensymphony.oscache.base.algorithm.LRUCache
cache.capacity=1000

Thanks in advance.