I'm going to guess you are talking about making an ejb call? For this, will need to make sure all classes that need to be loaded (e.g. the implementation class being passed), are contained on the classpath for the jboss server. Easiest way to do this is to include it within the deployment on jboss (e.g. if have a ejb deployment foo.jar, it includes the implementation class being passed).
Recently I found out, that the implementation of ObjectInputStream in JBoss (MarshalledValueInputStream) avoids a remote-loading of client classes, because it ignores the information, added by sun.rmi.server.MarshalOutputStream.annotateClass(). I guess, that is not a bug but has been made by full intention (security reasons?), so finally my stuff will not work.
Thank you anyway for your efforts.