[Serusers] 478 Error Response

Hi, I'm receiving 478 status for a REGISTER sent to SER Proxy. I'm sending Register request URI in the form of domain name. But 478 status code as given by SER is an invalid response as per RFC 3261. When does SER responds with status code 478? (Below is SIP register request packet and response packet) Is it configuration problem or any thing wrong in my packet? -------------------------------------------------------------------------------- Register Request to SER:--> Request-Line: REGISTER sip:ser.testlab.com:5060 SIP/2.0 Method: REGISTER Resent Packet: False Message Header Via: SIP/2.0/UDP 192.168.3.180:5060 From: <sip:1801@ser.testlab.com:5060>;tag=425215125 SIP from address: sip:1801@ser.testlab.com:5060 SIP tag: 425215125 To: <sip:1801@ser.testlab.com:5060> SIP to address: sip:1801@ser.testlab.com:5060 Call-ID: 1002330992425(a)ser.testlab.com CSeq: 1 REGISTER Contact: <sip:1801@192.168.3.180:5060>;expires=60 max-forwards: 70 Content-Length: 0 Response from SER: <-- Status-Line: SIP/2.0 478 Unresolveable destination (478/TM) Status-Code: 478 Resent Packet: False Message Header Via: SIP/2.0/UDP 192.168.3.180:5060 From: <sip:1801@ser.testlab.com:5060>;tag=425215125 SIP from address: sip:1801@ser.testlab.com:5060 SIP tag: 425215125 To: <sip:1801@ser.testlab.com:5060>;tag=a6a1c5f60faecf035a1ae5b6e96e979a-d8b4 SIP to address: sip:1801@ser.testlab.com:5060 SIP tag: a6a1c5f60faecf035a1ae5b6e96e979a-d8b4 Call-ID: 1002330992425(a)ser.testlab.com CSeq: 1 REGISTER Server: Sip EXpress router (0.8.14 (i386/linux)) Content-Length: 0 Warning: 392 192.168.3.198:5060 "Noisy feedback tells: pid=2361 req_src_ip=192.168.3.180 req_src_port=5060 in_uri=sip:ser.testlab.com:5060 out_uri=sip:ser.testlab.com:5060 via_cnt==1" -------------------------------------------------------------------------------- Thanks and regards, naresh