[Serusers] RTPPROXY doesn't work: HELP!!!

Hi everybody! I am running SER + RTPPROXY and I am trying to establish a call between a UA with public IP address and a UA with private IP address connecting to the proxy through a Access Point that has an extern ip address that is private too: UA1 (192.168.0.100) <--> (192.168.0.1) AP (192.168.1.1) <--> (192.168.1.2) SER (public IP) <--> (public IP) UA2 I just used the function force_rtp_proxy of nathelper module to force SER to change the sdp body of INVITE and reply messages, and in this way the fields c= and m= of the sdp get changed correctly. I can establish a call and the UAs send RTP packets to the rtpproxy. The problem is that the rtpproxy doesn't forward the RTP packets coming from the UA with public address (UA2) towards the UA with private address (UA1). Are there special flags I have to set in order to make rtpproxy work properly? Do I have to use other functions of nathelper module besides force_rtp_proxy? I am writing my own module for SER and I programmed it in such a way that the force_rtp_proxy function is called (not from the configuration file but from the module itself) for every INVITE request and reply, so that every RTP stream has to pass through the rtpproxy. If I try to use 2 UAs with public addresses everything works properly... Last question: how can I run rtpproxy in debug mode? And where can I see the log files??? Please someone help me! Thanks a lot! Chiara