asterisk users - Apr 2003 - ATA186: "Call/Leg Transaction Doesn't Exist" on local call

I know I've seen this reported already, and I can't remember the fix.

I have two ATA186s talking to an asterisk server.  When I call in on an 
outside line, both ring, and I can pick up either and talk.

But if I try to call from one of them to the other, the remote end rings 
just fine in both cases, but then as soon as asterisk bridges the two 
channels, the remote end sends a "Call/Leg Transaction Doesn't
Exist"
error and hangs up the line.

What am I doing wrong here?

Thanks.

B.

Here are the respective sip.conf entries:

[ata3]
type=friend
username=ata3
secret=asecret
host=129.91.0.164
context=home

[sjcata]
type=friend
username=sjcata
secret=anothersecret
host=129.91.0.161
context=home

In my extensions.conf:

exten => 83,1,Dial,SIP/sjcata|25
exten => 83,2,Voicemail,u100
exten => 83,3,Hangup

exten => 84,1,Dial,SIP/ata3|25
exten => 84,2,Voicemail,u100
exten => 84,3,Hangup

> But if I try to call from one of them to the other, the remote end rings
> just fine in both cases, but then as soon as asterisk bridges the two
> channels, the remote end sends a "Call/Leg Transaction Doesn't
Exist"
> error and hangs up the line.
Apparently it doesn't like our reinvites for some reason.  Any SIP experts
out there able to figure out why the ATA doesn't like them?  the Pingtel
seems to be okay with them.

Mark