Need information about proxying

Hello I am trying to using Freeradius1.1.0 I want to use it as a proxy to an external RADIUS server. In such a setup, if my external server is not up, and if I proxy a request to it, then I get back a access-reject, from my proxy radius server. Also If the username/password mismatch on external server then also I get a access-reject. Is there a way I can differentiate between these two? I mean is there a way I tell if the external RADIUS server is down OR Authentication at external RADIUS server has failed? Please please help in this regard. -Vishwa.