[Serusers] Is there something weird about this INVITE ?

One of our clients, using a Nokia E90, is having problems connecting to anything. His INVITE looks like this: U 123.236.98.24:55031 -> 11.22.33.44:5060 INVITE sip:1747XXXXXXX@our.proxy.com;user=phone SIP/2.0. Route: <sip:our.proxy.com;lr;transport=UDP>. Via: SIP/2.0/UDP 192.168.1.229:5060;branch=z9hG4bK3e89pocn1m7mkuiefdjljsj;rport. From: <sip:1101XXXXXXX@our.proxy.com>;tag=ls57mprkkdhc7kku07de. To: <sip:1747XXXXXXX@our.proxy.com;user=phone>. Contact: <sip:1101XXXXXXX@123.236.98.24:55045;transport=UDP>. Supported: 100rel,sec-agree. CSeq: 980 INVITE. Call-ID: pyBXpNNeoIcFBM7qVqVKrBneC2kxeM. Allow: INVITE,ACK,BYE,CANCEL,REFER,NOTIFY,OPTIONS,PRACK. Expires: 120. Privacy: none. User-Agent: Nokia RA-6 V 07.24.0.3. P-Preferred-Identity: sip:1101XXXXXXX@our.proxy.com. Max-Forwards: 70. Proxy-Authorization: Digest qop=auth,realm="our.proxy.com",nonce="46a713c0c887788778a731de0355c04db1896d23",algorithm=MD5,username="1101XXXXXXX",cnonce="0dad64affaabb2fa9c93611ec864e363",nc=00000001,uri="sip:1747XXXXXXX@our.proxy.com;user=phone",response="197f8a8b4b3d39281a147c2d9d2b6a28". Content-Type: application/sdp. Accept: application/sdp. Content-Length: 447. . v=0. o=Nokia-SIPUA 63353630343979125 63353630343979125 IN IP4 123.236.98.24. s=-. c=IN IP4 123.236.98.24. t=0 0. m=audio 49152 RTP/AVP 96 0 8 97 18 98 13. a=sendrecv. a=ptime:20. a=maxptime:200. a=fmtp:96 mode-change-neighbor=1. a=fmtp:18 annexb=no. a=fmtp:98 0-15. a=rtpmap:96 AMR/8000/1. a=rtpmap:0 PCMU/8000/1. a=rtpmap:8 PCMA/8000/1. a=rtpmap:97 iLBC/8000/1. a=rtpmap:18 G729/8000/1. a=rtpmap:98 telephone-event/8000/1. a=rtpmap:13 The server received this packet, but never responds to it. It simply never sends a reply. It's as though it doesn't recognise this as a proper INVITE. The ONLY thing I noticed about this that's completely non-standard, is that every other packet seems to have this period after it (indicating, perhaps, the end of a line... I don't know enough about the display of ngrep to tell). This INVITE does not. It goes almost immediately into the next packet, and it's almost as though this one never ends. Has anyone seen this before? Is there anything weird about this INVITE that would cause SER to ignore it? N.