asterisk users - Feb 2010 - "Unexpected message received" when receiving Fax

Hello,

I have been trying to setup asterisk 1.6.2.0 to receive fax. I have
two SIP trunks connected to asterisk. One of them is a VoIP service
provider and the other is an audiocodes gateway connected with pstn
and fax lines. I am able to receive faxes on the DID numbers provided
by the VoIP service provider, but I am not able to receive fax through
the fax lines connected through audiocodes.

udptl debug shows T.38 packets coming from the audiocodes, but the
line gets disconnected with an error
    phase_e_handler: Error transmitting fax. result=13: Unexpected
message received.

What could be the reason for this error? Is this a problem with
misconfiguration of audiocodes or asterisk.

I have the following t.38 settings in sip.conf
    't8pt_udptl=yes,redundancy,maxdatagram=400'
and the dialplan I use is
    exten => s,1,Answer
    exten => s,2,Wait(3)
    exten => s,3,ReceiveFAX(filename)

Thank you