IAS acting as Proxy

Hi folks, we have the following scenario: Radius-Client (Checkpoint-Firewall NGX) -> IAS-Agent (Windows 2K3) acting as Proxy -> Freeradius-Server (1.0.2) All authentication requests are denied by the Freeradius-Server. It seems that Freeradius cannot read/decrypt the password sended by the IAS, because in logfile the password is like "\226\231\....." Is there any special configuration needed for this scenarion? btw: the scenario without proxy (Radius-Client -> Freeradius-Server) works perfectly... best regards and thanks