Yikes.. it's difficult to say what the exact source of your problem is without more information.
I would suggest a couple of places to look.
Are all your objects being returned by the RPC call serialized?
In my project we found the best type of objects to pass to the client are just plain old
java objects (POJO's). If you can boil all your class fields down to primitives like
String or int it works even better.
Remember the only thing
you should be passing down to the client is the absolute minimum information needed for the Presenter (if you are using the MVP
pattern) to render the display. Any business logic or complex calculations should be done on the server before generating your response.