asterisk users - Feb 2010 - 500 Internal Server Error on Cisco 7940 after INVITE

Hi,

Our Cisco 7940 phones on a single network sometimes seem to drop calls 
as soon as they are picked up. After a second INVITE the phone sends 
'500 Internal Error'. One phone thinks its still in a call (though there
is no audio) while the other phone is not in a call.

The drop happens immediately after connecting and I think it is due to a 
second INVITE. Turning reinvite off seems like it fixes the problem but 
I haven't tested enough to be sure yet. The bug only seems to happen on 
the first time a call is made after a period of time (and even then only 
occasionally). Successive calls between the same phones are always fine. 
That makes debugging it a bit of a pain.

I have managed to capture a packet trace between * (10.200.4.100) and 
the 7940 (10.200.4.66) showing the error.

36.437814 10.200.4.100 -> 10.200.4.66  SIP/SDP Request: INVITE 
sip:3066 at 10.200.4.66:5060;transport=udp, with session description
  36.584594  10.200.4.66 -> 10.200.4.100 SIP Status: 100 Trying
  36.720893  10.200.4.66 -> 10.200.4.100 SIP Status: 180 Ringing
  43.211744  10.200.4.66 -> 10.200.4.100 SIP/SDP Status: 200 OK, with 
session description
  43.212001 10.200.4.100 -> 10.200.4.66  SIP Request: ACK 
sip:3066 at 10.200.4.66:5060;transport=udp
  43.212536 10.200.4.100 -> 10.200.4.66  SIP/SDP Request: INVITE 
sip:3066 at 10.200.4.66:5060;transport=udp, with session description
  43.304295  10.200.4.66 -> 10.200.4.100 SIP Status: 500 Internal Server 
Error
  43.304489 10.200.4.100 -> 10.200.4.66  SIP Request: ACK 
sip:3066 at 10.200.4.66:5060;transport=udp
  43.402253 Cisco_76:a5:0f -> Broadcast    ARP Who has 10.200.4.100? 
Tell 10.200.4.66
  43.470520  10.200.4.66 -> 10.200.4.100 RTP PT=ITU-T G.711 PCMA, 
SSRC=0xFA576B7, Seq=2616, Time=414864, Mark

There is a description of an error 
http://lists.iptel.org/pipermail/serdev/2005-November/006344.html which 
seems similar but since its in 2005 I assume the problem would be fixed 
by now. If that is the problem, can anybody suggest a workaround?

I have upgraded the phones to the most recent firmware (POS3-08-11-00) 
and * is "Version: 1:1.4.21.2~dfsg-3+lenny1" (debian).

Can anybody offer any advice or suggestions on fixing or debugging this 
further? If anybody else has encountered the problem and knows of a fix 
that would be great.

Thanks,

Ian Crowther
-- 
======================================================================Ian
Crowther           Tel: +44 845 4501626  Unit 108, 10th Avenue,
IT Dept, Comtek        Fax: +44 845 4501627  Zone 3, Deeside Industrial
Network Systems UK Ltd                       Park, CH5 2UA, Flintshire
=======================================================================

<snip>
I have upgraded the phones to the most recent firmware (POS3-08-11-00)
and * is "Version: 1:1.4.21.2~dfsg-3+lenny1" (debian).
<snip>

That doesn't look like cisco firmware to me... Unless I'm mistaken. What
version are the phones on? (Settings => Status => Firmware Versions)

-Dave