Faxing through multiple Asterisk boxes

Hello,
i am currently trying to get t.38 working through 2 asterisk servers
i.e
t.38 modem(Zyxel) --> asterisk(sip)–>asterisk2(sip)–>Carrier(sip)

now i can get it to work with 1 server i.e:
t.38 modem(Zyxel) --> asterisk2(sip)–>Carrier(sip)
and i can get it to work with Callweaver

t.38 modem(Zyxel) --> Callweaver(sip)–>asterisk2(sip)–>Carrier(sip)

but for consistency and i also have another carrier that uses asterisk i need to get
t.38 modem(Zyxel) --> asterisk(sip)–>asterisk2(sip)–>Carrier(sip)
working

what i am finding is that the system is failing to negotiate the t.38 and drops the call
here is the drop
[Jun 19 14:36:20] WARNING[15518]: chan_sip.c:3075 retrans_pkt: Maximum retries exceeded on transmission 5e87e3c77e58a010658b24130974177c@myserveraddress for seqno 961601 (Critical Response) – See doc/sip-retransmit.txt.
[Jun 19 14:36:20] WARNING[15518]: chan_sip.c:3102 retrans_pkt: Hanging up call 5e87e3c77e58a010658b24130974177c@myserveraddress- no reply to our critical packet (see doc/sip-retransmit.txt).

Any Ideas
p.s there is no changes in the backend box between using asterisk and callweaver.

Cheers
Darren

Just a question, I am getting “no reply to our critical packet” only when I use Gafachi as the provider for t38. Is the provider you are getting the error from Gafachi also?

No i am not using your t.38 provider.
I am using wholesale accounts

It appears to happen when talking to other asterisk machines.

it also may be related but i have noticed faxing through multiple asterisk boxes on sip g711 also fail
however
sip g711 -> iax g711 -> sip g711 works

This was a timing issue .

I.e Dahdi was not working properly