[SR-Users] Kamailio/RTPProxy incorrect port 0

Hello, I can't figure out why Kamailio reports hundreds of calls with the following error: "/usr/local/sbin/kamailio[2997]: ERROR: rtpproxy [rtpproxy.c:2727]: force_rtp_proxy(): incorrect port 0 in reply from rtp proxy" It seems that each time this error occurs, we got a one-way audio call. I already check and increase the limit for opening files that the process can open with ulimit -n 500000. But, anyway, if I look to /proc/$PID/fd, I never see more than 1000 files open. I also check the socket with netstat: same; I can see the error while there's only less than 800 sockets open. Is someone know what can be the trigger of this? Regards, Igor.