asterisk users - May 2006 - No audio in either direction on Zap -> SIP or SIP -> Zap calls

Hey,

Im running Asterisk 1.2.2 and im having problems with the audio when
bridging calls between the zap interfaces and sip.  zap to zap work
fine, as do sip to sip (but asterisk isnt in the media stream, as it
doesnt need to be) and terminating the call and playing a test message
via either sip or zap work fine.

Basically, the only time I see this problem is trying to bridge between
sip and zap.

At the packet level, I can see the packets leave the sip phone and get
to asterisk, but asterisk doesnt attempt to send any rtp back toward the
phone.  This is the same with iptables running or not.

If anyone could give any suggestions they would be gratefully received.

Ive included sections of relevant config files below.  At the very
bottom Ive pasted an extract from the * CLI with real numbers changed
for fake ones, and I notice that a native bridge doesnt actually get
mentioned.

zapata.conf:
[channels]
language=en 
context=zap
signalling=pri_cpe 
switchtype=euroisdn 
pridialplan=unknown
calleridusecallerid=yes 
hidecallerid=no 
restrictcid=no 
usecallingpres=yes
musiconhold=default
group = 3
channel => 63-77,79-93

sip.conf:
disallow=all
allow=alaw
allow=ulaw
[sip_proxy]
type=friend
context=foobar
host=sip.proxy.net
defualtip=x.x.x.x
port=5060
disallow=all
allow=ulaw
canreinvite=no
nat=no

extensions.conf:
[sip]
exten => _X.,1,Dial(Zap/g2/01234567890)
[zap]
exten => _X.,1,Dial(SIP/1234@sip_proxy)


Asterisk CLI:
    -- Accepting call from '1234' to '5678' on channel 0/23,
span 3
    -- Executing SetTransferCapability("Zap/85-1", "SPEECH")
in new
stack
    -- Setting transfer capability to: 0x00 - SPEECH.
    -- Executing Dial("Zap/85-1", "SIP/3456@sip_proxy") in
new stack
    -- Called 3456@sip_proxy
    -- SIP/sip_proxy-57c5 is ringing
    -- SIP/sip_proxy-57c5 answered Zap/85-1
    -- Channel 0/23, span 3 got hangup request
  == Spawn extension (zap, 5678, 2) exited non-zero on 'Zap/85-1'
    -- Hungup 'Zap/85-1'

--
  Mark Fisher