We are using this XML-JAVA Based Workflow tool (Flowbuilder3.0 from Trilog) in our app, that uses its own class loader. When we use this with hibernate we generally get "ClassCastException" on objects retrieved by hibernate and "No persister found for ..." during save.

Is there a way to specify which classloader to use to hibernate during session configuration or at some other time???

I'd say that Hibernate uses the classloader of the current running thread.