how to assign compsite keys manually

[vamshidhar nimbagiri]

i am using hiberate session.save() method and passing my mapping class object which contains the composite key.
hibernatesession.save(myclass); but its trhowing an exception saying

org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.wpsmedicare.corporate.entity.medicare.MedicareProvider
at java.lang.Throwable.<init>(Throwable.java:59)
at java.lang.Throwable.<init>(Throwable.java:73)
at org.hibernate.exception.NestableRuntimeException.<init>(NestableRuntimeException.java:100)
at org.hibernate.id.Assigned.generate(Assigned.java:32)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:85)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:481)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:476)

I have two classes one my mapping class and compositekey class which contains the composite fields info. plz tell me how to set this composite keys before inserting or calling save() method.

Thanks in Advance,
vamshidhar