Voicemail / MOH / Echo calls quiet after 20 seconds

Hi guys,

I have a problem with my * box where when I call in for voicemail, or really anything that is generated from the box like moh, or echo test, it goes quiet after around 20 seconds, give or take a few.
Have noticed something in the SIP logs which says:
“Scheduling destruction of call ‘000f8fa4-9491003b-7eebca6f-7a5af7­ 16@’ in 15000 ms”

After about that time i get:
Destroying call ‘000f8fa4-9491003b-7eebca6f-7a5af7­ 16@

The server is internal and has no need for any nat traversal, all clients are internal.
let me know if you need a look at any configs. Cheers.

Edit: K i just found a better description of my problem bugs.digium.com/view.php?id=9335 has anyone else had this issue at all?

I should point out that as I said before the entire network is internal, I am however in the UK and the asterisk box is near Byron Bay, so the latency ends up at about 400ms. I am using a gre tunnel from here to there, no traffic between here and there runs outside the tunnel so there are no NAT issues. I am using a Cisco 7940 at this end, other phones local to the boxes are grandstream.
All other calls work fine, only calls to Voicemail and Echo and i pressume anything else terminating on the asterisk box.

After checking the /var/log/asterisk/full file I saw the following entries at the time the call goes quiet or hangs up.

Aug 12 13:21:27 WARNING[2397] chan_sip.c: Maximum retries exceeded on transmission 000f8fa4-94910054-121be833-4421d53f@ for seqno 102 (Critical Response)
Aug 12 13:21:27 WARNING[2397] chan_sip.c: Hanging up call 000f8fa4-94910054-121be833-4421d53f@ - no reply to our critical packet.

no ideas anyone?