[Users] Can not register to OPENSER

Anyone knows why I keep getting following error message? Aug 2 13:10:26 localhost openser[30695]: ERROR: extract_body: message body has length zero Aug 2 13:10:26 localhost openser[30695]: ERROR: force_rtp_proxy2: can't extract body from the message I turn on nathelper, and saw from the following source code: int extract_body(struct sip_msg *msg, str *body ) { body->s = get_body(msg); if (body->s==0) { LOG(L_ERR, "ERROR: extract_body: failed to get the message body\n"); goto error; } body->len = msg->len -(int)(body->s-msg->buf); if (body->len==0) { LOG(L_ERR, "ERROR: extract_body: message body has length zero\n"); goto error; } Why do we care about the content-length, which normally is 0 for most of the SIP UAs? Following is an example SIP UA Registration and you can see "Content-Length: 0" in the bottom: Session Initiation Protocol Request-Line: REGISTER sip:sip.mycompany.com SIP/2.0 Method: REGISTER Resent Packet: True Suspected resend of frame: 62339 Message Header Via: SIP/2.0/UDP 192.168.254.6:5062;branch=z9hG4bK0997e90280d2f8e5 From: "Bill Office Phone" <sip:8001@sip.mycompany.com>;tag=ec200436c1169e42 SIP Display info: "Bill Office Phone" SIP from address: sip:8001@sip.mycompany.com SIP tag: ec200436c1169e42 To: <sip:8001@sip.mycompany.com> SIP to address: sip:8001@sip.mycompany.com Contact: <sip:8001@192.168.254.6:5062> Call-ID: 5a2ae3a1b883568f(a)192.168.254.6 CSeq: 20113 REGISTER Expires: 120 User-Agent: ABC 1.0.0.0 Max-Forwards: 70 Allow: INVITE,ACK,CANCEL,BYE,NOTIFY,REFER,OPTIONS,INFO,SUBSCRIBE,UPDATE,PRACK,MESSA GE Content-Length: 0 Thanks in advance. Best Regards, Bill Zhang