[Users] rport error

Hi all. I've a problem with a call using mediaproxy. The call got established, but after a few seconds got disconnected and I obtain the following errors. The problem appears with several clients. Please can someone enlighten me on where I err? TIA Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: parse_via: invalid port number <12797rport> Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: parse_via on: <SIP/2.0/UDP 213.144.x.x:12797rport;branch=z9hG4bK510915090^M Route: <sip:213.215.x.x;ftag=274138964;lr=on>^M From: <sip:marco@domain>;tag=274138964^M To: <sip:000000@voip.domain>;tag=5E97045-71F^M Call-ID: 408923322(a)213.144.x.x^M CSeq: 21 ACK^M Contact: <sip:marco@213.144.x.x:12797^M Max-Forwards: 5^M User-Agent: Linphone-1.0.1/eXosip^M Content-Length: 0^M ^M > Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: parse_via parse error, parsed so far:<SIP/2.0/UDP 213.144.80.48:12797rport;branch=z9hG4bK510915090^M > Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: get_hdr_field: bad via Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: bad header field Nov 8 23:43:20 fw /usr/sbin/openser[11625]: ERROR: parse_msg: message=<ACK sip:0000000@10.10.10.10:53429 SIP/2.0^M Via: SIP/2.0/UDP 213.144.x.x:12797rport;branch=z9hG4bK510915090^M Route: <sip:213.215.x.x;ftag=274138964;lr=on>^M From: <sip:marco@domain>;tag=274138964^M To: <sip:000000@voip.domain>;tag=5E97045-71F^M Call-ID: 408923322(a)213.144.x.x^M CSeq: 21 ACK^M Contact: <sip:marco@213.144.x.x:12797^M Max-Forwards: 5^M User-Agent: Linphone-1.0.1/eXosip^M Content-Length: 0^M ^M > -- In general, an implementation must be conservative in its sending behavior, and liberal in its receiving behavior. - Jon Postel (1943-1998)