asterisk users - Jan 2005 - sip channel between 2 asterisk box

I've setup a SIP channel between two Asterisk box, and use Manager API 
to generate some
calls. It's working quite fine, except this message (on the caller-side) :

Jan 10 18:18:09 WARNING[25046]: chan_sip.c:6805 handle_response: 
Forbidden - wrong password on authentication for INVITE to '"sip1"
<sip:asterisk@192.168.1.200>;tag=as77e9ebbb'

But the call is going through and I can answer on the other side. Could 
someone give me some help about the meaning of this warning ? What am I 
doing wrong ?

Thanks.

Here my sip.conf  :

***BOX1***
[sip1]
type=friend
context=answer-script
host=192.168.1.100
canreinvite=no
username=sip1
md5secret=password

***BOX2 ***
[sip1]
type=friend
context=from-sip1  host=192.168.1.200
canreinvite=no
username=sip1
md5secret=password