Cathi,
Did you run code similiarto your sample? I've tryed every consevable varyation and it wont work. Is the sample c#? HostObject.RefBizObj doesn't show up via intelli senese.
the code below is one way I tryed it, but this wont run.
the referance I'm creating loCOntact, The Rules host oClient, oClients child is oContact


Dim loContact as Contact
oCOntact loCOntact = (oCOntact)me.HostObject.RefBizObj.Get(typeof(oContact));